Nah i'm pretty sure its not hardware error, this exact(?) issue happened on Vista with the graphics kernel mode driver, look on google for nvlddmkm.sys - nothing but problems
Same screen flicker, and those also result in a hard lockup, I had the problem myself with 170x series of nvidia Windows drivers, but 180 I remember cured me, problem did not occur for me with 7.
Anyway, I'm guessing it's the same root cause.... this is bs, how can they make the same sort of mistake on two independent platforms, and then not even have the balls to come out and admit how badly they screw up.
I ran the nvidia package for 10.6.4, (extracted packages and installed, replaced OpenGL Framework to compatible version) - Those were 19.5.8f03, I was able to reproduce the result, buttttt instead of the machine locking up, it recovered (first time ever)... I still had to restart because after I saw the same thing happen (same messages in kernel log) I could no longer use 3d apps, WoW just refused to work...
Now trying the vanilla unmodified 10.6.3 kexts, these are 19.5.1f01
Running 2 instances of world of warcraft on Ultra settings, trying to produce crash