The main thing to consider is are you going for a High def or Standard def camera. If you are going for a HD camera you could do with a quad core processor in your computer. If standard def a dual core will be fine. Buy the way Sony Vegas is now on version 10.
Working with High Definition video is probably the most intensive thing a computer will do, so the more powerful the better. There is a ton of HD cameras out there that can shoot good quality a lot depends on what you want to do and how much dosh you have got to spend.