be warned, While Vegas 8 can do that, it isnt "good" at it. I have never tried, but if you want something that is "better" then i would recommend a programm called Ultra. I dont know if you can buy it seperatly, (it comes bundled in Adobe CS3) If not, that I hear that Premiere and After Effects do a better job, but for a heftier price. Basically what I am trying to say is, yes there is green screen stuff, but it aint really good. I hear from people that it is a pain in the butt, and felt like they waisted their money.
Anyway, I bet you like Vegas. It sounds like you dont want it mainly for the green screen, so I would recommend it. Extremely user freindly. Hope you like which ever you get...