No problem with also being able to support VS 2005, but I think it would be a big mistake if it wasn't also compatible with VS 2003. If you have to make a choice, please stick with VS 2003.
I think a lot of us probably don't jump right on the bleeding edge releases from Microsoft. It's better to wait until SP/2 comes out, and the bugs are fixed. Otherwise, problems in VS 2005 might look like problems in your code.
I also suspect VS 2005 will be backwards compatible with VS 2003. But - VS 2003 will likely not be forwards compatible with VS 2005.
Bottom line - given the cost of Virtual Studio, I'm not about to trash my investment quite yet... It isn't quite as simple as upgrading to the latest version of DirectX.
Willy