I know I'm joining this conversation late, but I just wanted to mention something about Prescott temps. My Prescott runs hot as well... it idles around 53-55 C, and peaks out around 70 C (and that's even with a Zalman HSF!). I'm using an old case with questionable ventilation, so I'm pretty sure that's why my temps are up there.
Honestly, though, it's never given me a problem... no throttling, no sudden restarts, nothing of that nature, and my computer's been on pretty much 24 hours a day for almost two years now. If there's a processor that can handle temps like that, it's the Prescott.
Anyways, that aside, it does look like you had some other issues there besides heat, but the sudden freezes and restarts do sound very similar to issues my friend experienced with his overheating video card. I know a Prescott can handle 50 C, but I'm pretty sure your video card can't, so I'd be willing to bet that's not helping things any.
Best way to find out if that's causing problems... take the cover off of your computer's case, find a decently powerful fan (the kind you cool a room with), and position it so it's blowing away from your computer so it moves the hot air out of there. If you keep it like that for a little while and don't get the mysterious freeze/restart, that should at least help in pointing to a solution.
Anyways... like I said, I'm joining late, so I'm really not sure if you solved the restart issue... but in case you haven't, that fix helped my friend pinpoint his video card overheating issue, so it might help you as well.
Good luck!