Juxtapose, that is interesting that XP worked fine... and you have already disabled all power-saving features? If the computer wasn't compatible with 64bit then it would not have installed.

That hardware you listed is fully 64bit capable.
Is there any error messages showing up in your Event Viewer that are showing up with the freezes? I agree that it does not sound like the hardware, but I would still recommend checking the RAM by running two passes of this program:
http://www.memtest.org/ Unfortunately if you already installed your chipset and LAN drivers then I'm low on ideas, given that you mentioned you already updated all your drivers from the sources. You might make sure that HPET is set to 64 in your BIOS though, too while you're at it.