Wikipedia says that version 11 dropped support for XP, so you want version 10 or earlier.
http://en.wikipedia.org/wiki/Sony_Vegas
Don't take this the wrong way, but I suggest, if you have similar questions, that you try Google first. You ended up waiting 12 hours for something that took me 12 seconds to find. I'm not saying that to be critical; I'm really just trying to help you in the long run ("teach a man to fish" and all...).
