This can happen if you do a dist-upgrade these days. First GLX is working, after the dist upgrade it doesn't work anymore. That is awkward and besides who can do without wobbly windows and 6-desktops-on-a-cube?

The problem is that Squeeze has recently declared a few older nvidia cards as legacy. However, the detection that a particular card is legacy doesn't work yet. Secondly (but I am not 100% sure about that) it seems that the nvidia-glx driver is dependent on the new nvidia-kernel, and that kernel is not available in Testing, you have to get that from Unstable. But that is a known bug. (http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=549869)

There is a good manual here: http://wiki.debian.org/NvidiaGraphicsDrivers#Libraries, and the bug report points to this page. However, it doesn't work because the detection algorithm does not detect that some older cards are legacy and should not use the newest driver.

First you should visit the nvidia.com web site, specify your card and find out what the latest usable driver version is. When it is 185.xxx you can simply use the newest driver from unstable. If you must use a legacy driver, there are options to solve this, assuming your version is 173xx:

1. Use this page: http://wiki.debian.org/NvidiaGraphicsDrivers#Libraries and perform steps 1, 2, 3 as specified, but you have to issue this:
2. Do it according to the bug report:
Again, you might have to change to Unstable in your sources.list to get the correct versions.

jlinkels

for the 173 downgrade xorg!
for a 96 ?? downgrade and there might be a update to "NVIDIA-Linux-x86-96.43.13-pkg1.run" to a "43.14 " in the near future .

Why downgrade xorg?

jlinkels

This might be a useful addition.

When the kernel on your system is upgraded you need to run this command again:
However during this process dpkg will complain that
/lib/modules/2.6.xx-x-xx/nvidia/nvidia.ko
will be overwritten.

This is embedded in the script, even if this file is deleted, the script will complain. The solution is to watch carefully on the screen at which moment dkpg stops. It will specify which file cannot be installed, which is something like
/usr/src/nvidia-kernel-legacy-173xx-2.6.30-2-686_173.14.20-1+2.6.30-8_i386.deb

The solution is simple, after the module-assistant is terminated, run this command:
Obviously do this only when dpkg terminates because if this error. On other moments this force option can be dangerous.

jlinkels