If you are talking about VS2005 Beta2, it can be done ( I have it set up that way). But, I would suggest that if your
development machine is the only one you have that you not do that.  There is always a chance installng a beta could hose 2003 or
other apps. I would (and did) do a complete back up before installing.
If you have had Beta 1 on your machine, I would be sure it is gone completely. Otherwise, it will cause problems.  The best
scenario is to install on a seperate system.
It's just much safer to not take any chances with your critical software and code.
james

I agree with James. Although I've read several reports of success (read "no
issues yet") with VS2003 and VS2005 Beta 2 on the same machine, there are no
guarantees. I'd suggest using something like Virtual PC or setting up a new
partition (dual boot) to test with VS2005. That would minimize risk to your
development machine.