windows doesn't "run" on unix/linux... they're alternatives. for instance, you can have a betamax video or a VHS video. they both do a similar thing, but they're competitors and not compatable with eachother.
linux runs a variety of different desktops that look similar to the windows environment you'll be used to. KDE is a more popular one, and you can see a variety of screencaps at kdelook.org.
as for the mac, the latest version of the macs OS is called OS X. its unix based.
one system isn't "better" than the other, it all depends what purposes you have. windows is certainly bloated and crappy, BUT it is easy to use and the majority of commercial software is developed for the win32 environment. practically every good website you'll visit will use a Unix based server tho, not a windows based server. its different tools for different things.
if you're interested in *nix, then install a distribution of linux onto a spare pc, or a spare partition on your hard disk. distributions are like "versions", each differs from the other, and the most newb friendly distro is called Mandrake. its free, so look it up on google and see if it might interest you. its not for everyone, as the linux world is very different to windows (even if they might look the same on the surface) but there's only one way to find out