I know people are saying there are TM issues with these names, but honestly, you can use these domains. As long as your not trying to cause confusion with the TM holder, distinguish yourself from the trademark holder, and reduce any risk of people thinking your associated with Microsoft, among other things, you'll be fine.
You're usage can be protected under fair use rights...
You will have TM issues only if you use "windows" and "vista" words together in a domain name. If you use "vista" only you will not have any problem.
I think that some people here talks about that but they haven't any idea about TM issues.
Savillor is correct on this Microsoft for one could never secure the vista name they have already tried and failed. If they did then they could also have Tm over all the places around the world with the word vista in it.
As long as you do not have windows and microsoft in your name you will be fine.
Setting up a support forum is a great idea to that way you associate your self but only from a tips and discussion aspect.
I own some nice vista names too if we all build sites remember to PM each other to backlink and help each other out I think with our names we cover every topic there can be raised when vista releases hehe.