I know that there is a converter for the xbox360 that will let you attach a keyboard and mouse to it and use it for gaming. however, it aint cheap. £70 is the asking price.
http://www.xcm.cc/XFPS_3.0_Sniper.htm
having had both systems, i'd say there's little in it. xbox is "cheaper" on the initial outlay, but things like wireless adapters arent cheap. if you dont care about blu-ray, xbox is the way to go, if you do want blu-ray then ps3. also as stated ps3 has free on-line play but the xbox on-line system is more polished (in my view).