I have run Mac OS X 10.4 (Tiger) at school, and it isn't bad (ignoring the insane amount of cash they put out for ~20 new 23" iMacs, and about the same amount of aging PowerPC models). Safari is lacking, iMovie (normal and HD) falls on its knees to Windows Movie Maker (Vista's version, NOT XP's - forgot to mention that in my list above). It all looks pretty, but it lacks any kind of customization at all. Yea, you have your Dock (that can not be put @ the top with your... Apple Menu) and your Dashboard (that can be confusing for new users: I had to explain it to a few classmates personally). And the "Mac's are oh so perfectly secure" is all talk. I (inadvertently) scared the teacher into thinking that my iMac had a virus on it, because my portable hard drive malfunctioned! Talk about confidence in your products!
Mac is good, if you have the cash and don't want options.
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I have to agree with Mouser on the "fresh OS" thing; Vista still holds backwards compatibility for some DOS filenames and whatnot. WHY?!?! Sure it is just an option, but millions of others are sitting there, to be used once or twice by all of the users. Pointless bloat.
And UAC: I disabled it on all 3 Vista PC's in the house. If your into Linux and don't mind the administration popups for your password once in a while, for Vista do this:
Disable UAC -> Install everything and configure it -> Let Windows Update do its thing -> Clean up your PC and defragment it -> Reboot -> Enable UAC
It doesn't nag you THAT much, in comparison, and it can save you- personally, if I am on Windows, it is either web, IM, coding, or games. Not the time to ask if that new Xfire update installer can be Allowed or not. (And this PC has never seen a malicious program)
Old saying: Speed, price, quality - Pick any two. 
-40hz
Speaking for most of the internet: I'll take my 3: Speed, Quality, Torrent (I mean, wha...)

(I'm on legit Vista, don't send the feds after me!)

-Brandon
EDIT: I own 2 Linksys routers (one in use) with 2/3 of the wireless PCs using Linksys cards (everything is Draft-N

). I followed the instructions the first time I setup the old WRT54G... I never did that again. You gotta just plug everything in, head over to
http://192.168.1.1/, setup your options, and setup the computer's wifi. The instructions are pointless IMO.