Something else will be doing the A/D, definately not Vegas. Not to mention, there's probably not one VCR on the market with USB outs... LOL!
My guess is that you're passing through a DV cam to pull this off. Correct?
Also, you'll probably be capturing with the Capture App, not Vegas directly.
There's really nothing to do on the capture front because the A/D will be doing all of the heavy lifting, so you better hope your AD is good. After that, once captured, you can tweak, color correct, etc. if needed. But Vegas will ONLY bring in the DV from the source (whatever that is), Vegas won't do anything while capturing except to be a bit bucket from the USB to your HD.
BTW, the Vegas forum on DVInfo.net is your friend when it comes to Vegas...