Thanks for all the responses:
I am booted into 2.6.24-16-generic, which is correct I believe.
Are you 100% sure that you're booted into the correct kernel?
I also suspected it has something to do with kernel modules. I tried removing nvidia-kernel-common and nvidia-glx-new and then reinstalling. There was no effect. I then tried the 173.08 beta driver from the NVIDIA website, again to no effect.
I don't know exactly what's been suggested, but I had a similar problem. The old kernel module stuck around for some reason (I think I had the non free drivers installed manually previously). Try removing nvidia-kernel-common and nvidia-glx-new and re-installing. If that doesn't work, download the latest driver from NVIDIA and install that manually.
So I'm still in the same spot. Any other ideas?
I thought it was interesting that in Xorg.0.log, it shows the glx module being loaded:
I also thought it was interesting that in dmesg, there are three warnings about nvidia and sysctl, and also three gdm segfaults:
(II) LoadModule: "glx"
(II) Loading /usr/lib/xorg/modules/extensions//libglx.so
(II) Module glx: vendor="NVIDIA Corporation"
compiled for 4.0.2, module version = 1.0.0
Module class: X.Org Server Extension
ABI class: X.Org Server Extension, version 0.1
(II) NVIDIA GLX Module 173.08 Wed Apr 2 08:19:55 PST 2008
(II) Loading extension GLX
Hope this info is useful, and thanks again to all who have responded.
[ 467.263817] gdm: segfault at 800690b68 rip 7fd2fc581d1f rsp 7fff07ddca50 error 6
[ 590.785835] gdm: segfault at 800691918 rip 7fbed99f7d1f rsp 7fffe52532c0 error 6
[ 624.897281] warning: process `nvidia-installe' used the deprecated sysctl system call with 1.23.
[ 624.897289] warning: process `nvidia-installe' used the deprecated sysctl system call with 1.23.
[ 624.956318] nvidia: module license 'NVIDIA' taints kernel.
[ 625.209763] ACPI: PCI Interrupt 0000:01:00.0[A] -> GSI 16 (level, low) -> IRQ 16
[ 625.209770] PCI: Setting latency timer of device 0000:01:00.0 to 64
[ 625.210384] NVRM: loading NVIDIA UNIX x86_64 Kernel Module 173.08 Wed Apr 2 07:55:48 PST 2008
[ 625.233009] warning: process `nvidia-installe' used the deprecated sysctl system call with 1.23.
[ 770.327503] gdm: segfault at 800689f98 rip 7fc986fa1d1f rsp 7fff927fb8e0 error 6