Frequent hard lockups with white screen

This bug has partially been referenced here: https://bugs.launchpad.net/ubuntu/+bug/109643

I am submitting a new bug, since I think that the problem is unrelated to any specific video driver.

Summary:

Using Fiesty stable, upgraded from Edgy, I am experiencing frequent hard lockups. When it crashes, I get a a pattern of the screen at crash, repeated multiple times across the screen, with white lines and a skew.

The problem occurs in both edgy and feisty, with vesa drivers, and nv, and the closed source nvidia drivers. I don't think it's overheating; my motherboard has a processor stepping feature, and it has happened at reduced processor speeds (and my machine is well ventilated).

The problem went away after I disabled processor stepping (AMD Cool'n'Quiet) in the BIOS. I suspect that the issue is a kernel problem -- I ran feisty beta for a while with no issues, it was in the last two weeks of testing the issue cropped up (with [i think] a kernel update). The issue is not reproducible (except in the sense that turning off processor stepping fixes it); it occurs seemingly at random, even at very low processor loads.

SSH is inaccessible, and I cannot restart the X server.

Hardware Profile:
Biostar Geforce 6100-m9 Motherboard (On-board Geforce 6100 video)
AMD Athlon 64 3400+ Venice
1GB PC3200 Memory

Several complaints that seem to be related have been discussed in the forums here:
http://ubuntuforums.org/showthread.php?t=405993 and
http://ubuntuforums.org/showthread.php?t=402580

I also experienced the issue with Edgy (and so have others, if you look at the forum post), but only after updating to the latest packages.

I would like to help in any way possible, so let me know what information I can provide. The issue also occurs with SuSE 10.2 on the same hardware.

I am currently running: 2.6.20-15-generic #2 SMP Sun Apr 15 07:36:31 UTC 2007 i686 GNU/Linux