Is it possible within Vegas Video to create masks or mattes that follow a particular object AND are shaped like the object? I know this is often done by hand as rotoscoping. Can that be done in Vegas, or would the footage need to be opened in some other kind of program?
If chromakey is not an option (and it usually won't be unless the video was shot for chromakeying), you'll probably need to dump the file off to another app and create the mask externally.
You might try SF Viscosity- you can paint right on the frames and use that as a tracking mask. Viscosity does not support DV avi, but uncompressed avi will work. You might try rendering out an uncompressed avi file at 50% original size- often that's clean enough for a mask.