Well QE, I'll respond to you since no one else has. The reason why no one else has is because there are multitudes of reasons why you're experiencing problems and no one knows where to start helping you since you were pretty vague on your problem.
A few questions to you:

7.0 which version a, b, c, d, so on
64 bit Vista or 32
Clean install of Vista or upgrade from older OS
Legal version of Vegas or Cracked
Computer CPU
Amount of ram
Free hard drive space
and so on and so on

As you can see, there are a LOT of variables. Are you new to video editing? Ever use Vegas on a working system? Migrating from a different NLE, Pro, Hobbyist, and on and on.

Try giving us some info. There are some very experienced and knowledgeable folks around here that may be able to help. I might also add that you may do some searching on this forum because lots of topics have been discussed that may help you.

Gotta start somewhere I guess. Come back with a few more specifics and good luck.

Mike