I would play normally and record a demo. Then play your demo and record it with fraps at 60 fps if you can handle it if not then 30 fps. That'll give you the cleanest solution. Fraps videos should go straight into vegas, if not there are plenty of ways to convert/alter it including xvid, virtualdub, avisynth(for scripting quality), and programs like xilisoft video converter. Some of them are free some of them are not, sometimes you can find free alternatives for them.