Out of curiousity, did your PC come with Vista, or did you upgrade?
From what I’ve heard, the current version of Vista is very unfriendly towards video editing tasks, and a brand new machine running it has the proclivity towards fatal crashes when some video work is being done.
If there’s a way to downgrade your OS to XP, it’s very likely that this will solve at least the crashes you’re experiencing. If not, I’ve heard that adding RAM helps, as Vista is a memory hog.
Sorry if that’s not what you’re looking for, but it’s a first step.
