Tim, not to threadjack too badly here. (By the way, my user name is supposed to be Soundgod, but something happened during registration)
My problems most definitely are not dodgy clips. I'm working with fully finished Vegas rendered projects. Also, it is very doubtful that it's a new incompatibility issue of hardware and software as my clips were rendered on this very machine using both Vegas 6 and 8. There has been no new hardware added in around 2 years. That is what is leading me to think it's some sort of issue with the motherboard itself.
Back to Yam Jam though.
Yes, you probably do need to try rendering out each of your clips as either an AVI or WMV by itself to see if one of them is the problem. Hopefully you will be able to sort out your problem that way. Of course the next step after that will be the clean install of Vegas, which tends to be a pain.