PC locks up after less than a minute in-game

[Xashren]

Title says it all, really: after roughly a minute in-game my screen freezes, the mouse locks up, the audio stutters then dies. The task manager can't be opened, leaving no alternative but to reboot the machine.

I'm on an Intel quad-core machine running Vista 64, which apparently causes all sorts of issues I've spent the last few hours correcting one by one. To preempt the "read the stickies" posts, I've applied every solution in the Dual / Quad Core CPU Fixes OP, plus setting up RunFirst and ensuring that CPU Affinity is set to 0. I'm running a legitimate copy of the Titanium client as per instructions for the server I'm connecting to, and the drivers for my video card (an Nvidia GTX 295) are up to date as of May 6th.

All I can think of is that there may be some conflict with the video card or my display settings. I've set the client to run in Windowed mode at 800x600, which has allowed me to at least get in-game, but the lock-ups continue.

Any thoughts?