All depends on what you want to do
VS 2003 wont code against the .NET Framework 2.0 just like VS 2005 won't code/compile against .NET Framework 1.1
So if you are looking to code right now, then Studio 2003 would do that.... if you are looking to jump into the new Beta stuff, then wait
Both Studio2003 and Studio2005 will run side by side
Why do we drive on a parkway and park on a driveway?