I have the same issue with the ATI x600 AIW as well as an Antec 430 Truepower PSU, and I'm going NUTS.
I've tried loading, unloading, and reloading drivers for three days now, and I can't get this thing to stop hanging. On top of that, I have an issue where the machine won't shut down. It hangs there too. I was running Nvidia RAID 0 with two 120 GB Seagate drives, but after I broke the mirror, the thing finally shuts down.
What do you think? Is it ATI or Nvidia?
AMD 64 3500+
2x512 Crucial Value Mem
ATI x600 AIW
One seriously bummed out guy.