This seems to be the exact same problem reported about RC1 by Marc last year.
I have tried reformatting my drive, installing XP (with no additional
software/drivers), then upgrading to Vista. Once upgraded I installed the
graphics drivers and windows updates. There's no usb devices attached, no
printers installed, no bluetooth. But the system still freezes periodically -
doesn't usually last more than 15-20 minutes.

Ian