HTP for Gaming?

Hi guys, I was wondering is it possible to build a HTP that will play the latests game like need for speed the run?

I would like to build something that I can put under the tv and that will allow me to play the latest games using a wireless controller of some sort.

I'm just wondering firstly, what sort of O/S would I go for? Windows Media Centre or Windows 7?

If it is windows 7 then I would need a nice XMB(Front End).

Anyone built anything like this or can give advice please.

mATX or a decent ITX board + Win 7 + XBMC + 360 receiver + wireless keyboard and a laptop mouse?

Windows 7 contains media center so no need for a front end, particularly since its better than the version in XP MCE.