I have just learned that Inventor 2008 runs fine in Windows Vista but Autodesk will not officially support it in Vista though. And there will be no native 64-bit Inventor yet. We have to wait.
I don’t know why Autodesk doesn’t fully support Inventor in Vista. In any case I will probably use Vista on my Inventor 2008 box. What I have seen makes me confident that it will run fast enough – and much faster than e.g. Solidworks in Vista which is slow as hell (which is claimed to be Vista compatible btw).
Inventor 2008 should be out next week.