It's really pretty good now on new PCs. Vista got a lot of bad press two years ago when people tried to upgrade two year old systems (4 years old today) - and the systems just struggled to run Vista. Today with dual core the minimum and quad core very common (except on Apples), and 256 MiB to 512 MiB graphics cards the norm - Vista runs great.
Windows 7 is shaping up to be a nice improvement -
you should download the beta and try it out. It probably won't make you give up your Apple - but you may think "oh, Microsoft does learn from its mistakes."
(ps: I jumped on Vista right away - but since I was able to get a dual quad-core Xeon with 16GiB of RAM and two Nvidia Quadro graphics cards it ran fine from the start

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