I'd buy Vista
Do what I do, get yourself a lovely new iMac and then use VMWare to run Vista on it alongside the iMac's OSX. I flip back and forth between them all day long. The mac hardware is the best anywhere, the machine is a work of art. I see it on my way out the door every day and looking at it makes me feel happy and optimistic. When's the last time a machine did that for you?
But, to be honest, Mac's operating system is way overrated. I actually prefer Vista, and Windows XP is pretty awesome by itself. In the old days, Apple really had it over Windows for ease of use. But that's an old reputation, Windows passed up mac a long time ago. Microsoft copied mac's best features, made them better, and added a few of their own. I find Windows much easier to use, and I put some pretty heavy use on it as a technical writer and a trainer, working on sometimes 7 or 9 different applications at the same time, flying back and forth between them all and carrying text and graphics back and forth. It's much harder to do the same thing on a mac, the interface just isn't as well built for serious work, things take two clicks where Windows does it in one. Windows has just had a lot more resources pumped into refining it than a much smaller company like Apple could compete with.
And if you can't or don't want to afford the mac hardware, just get a PC and feel good about your choice.
