This is happening to me as well, 2 separate builds, in fact I thought it was duff memory in the older pc that made me upgrade to i5. The only things that are the same in that build are 880 GTS, PSU and hard drives.
I read elsewhere about the power settings, this seems to have helped a bit, also people mentioned it could be MSN messenger, I have disabled it and the freezes are less frequent now, sometimes I can go days without it happening, others it will happen 2 or 3 times a day.
It doesn't seem to be anything particular that causes it, although when i was using Firefox that seemed to cause it to freeze, however I have just been browsing folders or watching a avi film (sound still plays for a few seconds and then stutters and freezes) and it will do it.
Will probably revert back to Vista as this is a PITA, I'm still using the 7100 build however this was fine on my laptop before it died on me.
Dirtydog has that sorted your problem out? I haven't overclocked my system but I havent checked timings are normal.