Used: AMD 3500+
Used: 2GB Ram
New: FoxConn MB
Used: 6600GT VCard

My vista locked up very randomly as well, mostly during downloads but also during regular usage, browsing and especially trying to setup media center. After a copule of hours of cursing, i realized that it started locking up after i downloaded vista nvidia drivers/control panel for my 6600GT. so i reinstalled vista with format cause i had Windows.old folder which vista would NOT let me delete (another cause possibly) then i did NOT install any drivers AT ALL, i let vista get drivers for my TV card and wireless card and nothing else and its working fine NO lockups for about an hour now...before it would lockup within 1-5 minutes, i was able to download large fiels file and set up media center and no lockups. Hope this helps someone.