Softmodding an xbox is easy as pie. Search around on google. XBMC is the best media centre there is , Easily connects to windows shares for media. Alows you to backup games to the HDD. There are good versions of snes etc emulators so you can fill it with roms.
You can pick up seceond hand xbox for £10 and chuck a 250gig HDD in it for next to nothing. Its the way to go. Make the xbox such an amazing piece of kit.