with linux you'll need to do a little tweeking to get everything working the way your used to in windows (its all in the maya docs though)..when u install linux for example redhat, you have to choose which GUI your going to use, the basic ones are KDE and Gnome. You can even install both and decide which one you like better, maya will be installed on both dont worry...its just at the login screen you just select which one you want to login to. Basically with linux you have a TON of flexibility...any tweeking you can think of is possible. With mac (like windows) its pretty much install it and run it...nothing more...many people say that mac is much more stable, but with the power most new pcs are getting today the line is pretty invisible.
Also, you might want to wait until 2006 to get a mac....they're going to releasing there first intel based OS...which could mean you'll be able to partition with windows.