I'm a N00B so please excuse & correct if the steps I use to manually upgrade/downgrade BOINC on Linux, in my case Ubuntu Lucid Lynx, is faulty, lacking, or could be improved.

Step 1: download from BOINC sitehttp://boinc.berkeley.edu/download_all.php

Step 2: open terminal

Step 3: extract downloaded boinc file, in this case boinc_6.10.56_x86_64-pc-linux-gnu.sh

user@Domain:~$ sudo sh boinc_6.10.56_x86_64-pc-linux-gnu.sh

Step 4: change permissions

user@Domain:~$ cd BOINC
user@Domain:~/BOINC$ ls -l
user@Domain:~/BOINC$ chmod -R g-w,o-rwx *
user@Domain:~/BOINC$ chmod -R g+r locale*
user@Domain:~/BOINC$ chmod g+rx boincmgr
user@Domain:~/BOINC$ chmod g+rx lib*.so
user@Domain:~/BOINC$ ls -l

Step 5: stop boinc client

user@Domain:~$ sudo /etc/init.d/boinc-client stop

Step 6: copy over original BOINC files

user@Domain:~/BOINC$ sudo cp boinc /usr/bin
user@Domain:~/BOINC$ sudo cp boincmgr /usr/bin
user@Domain:~/BOINC$ sudo sp boinccmd /usr/bin

Step 7: copy over (Needed localization files in my case Danish)

user@Domain:~/BOINC$ cd locale
user@Domain:~/BOINC/locale$ cd da
user@Domain:~/BOINC/locale/da$ sudo cp BOINC-Manager.mo /usr/share/locale/da/LC_MESSAGES

Step 8: start boinc client

user@Domain:~$ sudo /etc/init.d/boinc-client start
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The issue with having to restart BOINC in Linux to avoid "GPU Missing" issue is still here, maybe for a long while.

Open Terminal & write:

sudo /etc/init.d/boinc-client restart

Here's a guide to get the latest Drivers for Linux, which aren't always available the easy way.

1) First step: you must reset the Xorg to its default conf. Before, you should backup it, to avoid any mistakes.

In the Terminal:

$ sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf.original
$ sudo dpkg-reconfigure -phigh xserver-xorg

2) Installing packages and dependencies:

$ sudo apt-get install build-essential linux-headers-`uname -r`

3) Remove old version drivers:

$ sudo apt-get --purge remove $(dpkg -l | grep nvidia | awk '{print $2}')

Download the driver from nvidia website. You must check your system architecture (x86, 64...)

4) In my case: Ubuntu 64:

$ wget ftp://download.nvidia.com/XFree86/Linux-x86_64/195.36.24/NVIDIA-Linux-x86_64-195.36.24-pkg2.run -O NVIDIA-Linux-195.pkg.run

5) Now, move the installer to /usr/src and link it. Follows:

$ sudo install NVIDIA-Linux-195.pkg.run /usr/src/
$ sudo ln -s /usr/src/NVIDIA-Linux-195.pkg.run /usr/src/nvidia-driver

Kill X:
6) Time to stop X on GDM. So, press "Ctrl+Alt+F1", login and stop gdm:

$ sudo /etc/init.d/gdm stop (If KDE is used write instead: $ sudo /etc/init.d/kdm stop)

Installing NVIDIA Driver
7) Installing:

$ sudo sh /usr/src/nvidia-driver

8) When it is done, restart your computer:

$ sudo reboot

After boot up, go to terminal and:

$ sudo nvidia-xconfig
(I didn't need to do this, but this step is in the origial step-by-step)

BTW, I got this from here: http://forums.nvidia.com/index.php?showtopic=99513 & changed a little bit.

To search for the latest Nvidia Driver, go to http://ftp://download.nvidia.com/XFree86/ to find what they have.

For all who wish to know, I have been told, but have yet to try, that XUBUNTU is the way to go for those who want to get the most crunching done. http://se.archive.ubuntu.com/mirror/cdimage.ubuntu.com/xubuntu/releases/10.04/release/ I've had trouble installing Ubuntu 10.04 on several PC's, but the way I go it installed on them was to use the "Alternate install CD", it's a text mode install which is guided & quite easy to use.

BTW, just my POV, BOINC doesn't have to be an expensive hobby. Especially if you use GPUGRID. It's not CPU intensive & AMD/Intel Dual & Quad Core CPU's are good enough, as long as you stock it up with Nvidia GPU's. PCIe Slots are also not dependent on that PCIe 2.0 x16. PCIe x8 is good enough, no SLI capability needed, DDR2 is good enough, if it's a crunchbox, any old HDD is good enough, & if you use a GT240 GPU you don't need a monster PSU. All you might need is good airflow & a little patience with Linux if it's something you haven't tried yet. So instead of a totally new PC, maybe an old one with a new GPU is enough.

Just to take it into extremes, it doesn't even require a Dual Core CPU, DDR2 or a HDD, just as long as you've go a PCIe slot for a cheap GT240, Linux 32bit can be installed on a USB stick (if booting from USB is possible), & you're good to go & getting more credits than everybody else crunching CPU only BOINC Projects.
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Thanks Liveonc for your tuto.
Just to add, you don't need the latest Nvidia release to crunch GPUGrid, thus you can simply use synaptic to install the Nvidia driver (After adding the PPA repository)

And also, about BOINC, I've never installed/upgraded BOINC is this way.
You can directly do a sudo chmod +x on the .sh script to be able to run it without the root permission. (Instead of using the command line to install it you can also simply go to the properties of the script and allow the execution of this one. Then a simple double click will execute the script.

And in my case, to launch BOINC at the startup, I add the command line: /where/is/theBOINC/folder/run_client to the start up of the session.

My solution is more for an install. (Possible to do the same for an upgrade anyway)
but the liveonc's solution is good too.

Enjoy crunching on GNU/Linux.

PS: Xubuntu is ligther than Ubuntu.
In my case, I have a crunch box, running only in command line (But no GPU), hence I have more memory left and less CPU used by the system.
If you want to do a crunch box with a GPU, you can try ligther GUI (OpenBox, Fluxbox, etc...instead Gnome/KDE/XFCE)
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MyUneo, the Cupid of Services

Thank you Dudumomo, it was you who got me started with Linux & how to get the supported drivers & Boinc Client when i didn't know how to.

I'm just trying to pick up from there. I'm still a N00B. There are still many difficulties & frustrations with Linux for me. I just started with Xubuntu, because it's still easy enough for a N00B like me. But even there, manually upgrading/downgrading drivers can't be done the same way. It only works for Ubuntu & Kubuntu. if I change xorg.conf by writing sudo gedit /etc/X11/xorg.conf fx to change the resolution at startup, it won't work for me either, plus i have to download gedit before I can even try. I didn't know this, & now I sort of regret I installed Xubuntu on all my Linux PC's.

What would happen if I tried OpenBox or Fluxbox, or just went command line? I don't even know how to remotely check if my PC's are running & I've had so much problem with PC's freezing or erroring out due to heat, Boinc Clients that won't startup detecting GPU's w/o having to be restarted, Drivers that eat up memory, Boinc Clients that don't start due to lacking memory, etc, etc. Wouldn't I have even more problems if I switched to something lighter or went command line?

But thanks for telling me how to install BOINC that way you showed, it's faster & easier, especially for testing Beta Boinc Clients that I'm not sure is good or bad.
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You did a very clear tutorial ! Thanks !

With the latest release of Ubuntu, Xorg works a bit differently.
But, just to let you know, on Xubuntu, you "need" to install gedit because this one is mainly for (I mean, already installed on) Gnome (Ubuntu). BUt on Xubuntu, you have a similar tool. (I think it's called "mouse")
So you don't need to use gedit in fact, to do the same.

If you got memory issue, yep, you might want to switch to something ligther. But for me, if my computer doesn't have a GPU, I only install Linux as in command line, thus, my system use a lesser amount of CPU clock, then a larger part is dedicated to BOINC. (For my crunch box I mean, but also my regular PC when i'm not using it, i just close Gnome)

But in your case, it is difficult to say if you are going to have more trouble or less by using a different interface.
However, I recommend you to keep using Xubuntu or Ubuntu, it is far more user friendly.
About your heat issue, this is very important ! Is it the GPU or the CPU ? For the CPU, you can try to undervolt it and still use the same freq if the system is stable (What I did) and be sure to get your fan at full speed (Especially the GPU)

You are very diligent and you participate a lot here with useful ressources !
I'm glad we are sharing our experience !
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MyUneo, the Cupid of Services

Just like Dudumomo said. The steps for upgrading/downgrading drivers manually doesn't work for Lucid Lynx, Ubuntu 10.04 I haven't yet found out how to. But I'm going back to Karmic Koala, Ubuntu 9.10 all my PC's fail GPUGRID WU's on 10.04

You did a very clear tutorial ! Thanks !

With the latest release of Ubuntu, Xorg works a bit differently.
But, just to let you know, on Xubuntu, you "need" to install gedit because this one is mainly for (I mean, already installed on) Gnome (Ubuntu). BUt on Xubuntu, you have a similar tool. (I think it's called "mouse")
So you don't need to use gedit in fact, to do the same.

If you got memory issue, yep, you might want to switch to something ligther. But for me, if my computer doesn't have a GPU, I only install Linux as in command line, thus, my system use a lesser amount of CPU clock, then a larger part is dedicated to BOINC. (For my crunch box I mean, but also my regular PC when i'm not using it, i just close Gnome)

But in your case, it is difficult to say if you are going to have more trouble or less by using a different interface.
However, I recommend you to keep using Xubuntu or Ubuntu, it is far more user friendly.
About your heat issue, this is very important ! Is it the GPU or the CPU ? For the CPU, you can try to undervolt it and still use the same freq if the system is stable (What I did) and be sure to get your fan at full speed (Especially the GPU)

You are very diligent and you participate a lot here with useful ressources !
I'm glad we are sharing our experience !