Windows 7 is supposed to support the same drivers as Vista, as they're based on the same code.
Also, Microsoft shouldn't be adding any bloat to the system from now on. They say that the beta is feature complete, meaning that there will be no new major features, just making the code more efficient.
I don't know if you consider the bloat to be things like Movie Maker and stuff, but these will now all be optional, and part of the Live suite, which you do not have to install, or you can just installed whatever parts of it you like.
Microsoft seem to be committed for Windows 7 to run on netbooks, so they are trying to make it a lot less processor intensive. So if your machine runs Vista well, then it should run Windows 7 even better.
As for time limits, the official beta will expire I think I read in August this year. There's also speculation that the final release will be around that time too, which wouldn't surprise me at all.
I got all this information from Paul Thurrotts podcasts, his website and random stuff from stumbleupon. If you're interested in it, you should check out Paul Thurrotts winsupersite website.
http://www.winsupersite.com/win7/
PS I am not sponsered by him or Microsoft
Just passing on the facts I know