NVIDIA & ATI currently have Vista driver sets. Avast the Antivirus of choice on Vista right now. I have run Adaware and spybot with no probs.
There are definite limitations though, most but not all Wireless network cards seem to be supported.
I recommend perusing the Technet forums to get technical answers:
Micros*ft Technet Forums
Expect your machine to use about 400 megs of RAM while idle, w/ about 42 processes running.
So far my personal opinion is that MS has a long way to go before Vista is my default OS. For all the visual stuff you might as well get WindowsBlinds.