Thanks for the help!
I'm running into new problems though...I am frameserving the MPEG from Sony Vegas into Virtual Dub. I have tried encoding using both Lagarith and another lossless codec called MSU.
For both, I import the new file into Vegas, and slowly, the video drifts out of synch with the original MPEG. Does anyone know why this could be? Does VirtualDub not work well with frameserving as input? Thanks