For those of you that care (and didn't already know)... You can hook your XBOX 360 controllers to your PC (they are USB after all) and they work great with MAME.
I don't own a 360 yet, but I got a controller for free at Microsoft Meltdown and Windows XP detected it immediately with no driver download required. I liked it so much, I bought a second one the other day as an early birthday present. I have them both hooked up to my main machine at the moment.
Whenever I finally get a 360, I'll be ready... :)
36th Birthday in 3 days (Thursday)... feel free to send me a 360!