Sorry, I shoot in and out of this forum when its existance pops up in my mind.
So uh, if you're frapsing at 1024x768 half size (which I don't recommend, 1280x960/1024 is what you need for fair quality at half size), you want to set vegas to 512x384 (1024/2 and 768/2).
If you have any specific questions you're always welcome to ask.