I have actually scored an original Xbox a few weeks ago. Modded it as soon as I got it using the "Hotswap" method. I also bought a 120 GB IDE drive for it off the classifieds and am REALLY loving it. The ability to save games to the hard drive and backup the family photos to it is great. XBMC is wonderful, though I really wish I could get the Youtube plugin working.

I wrote a little guide to the guides on doing the hotswap method here:

http://www.facepunch.com/showpost.php?p=13461851&postcount=0

You can do this method without buying anything, assuming you own a Torx screwdriver.