good thinking - did u consider buying a modded xbox? (or modding an xbox u have)
it can do pretty much what u need and play games .
http://www.premodded.com is a good example but there are others.
the xbox can run a special version of MC as well called xbox media center but u may alreayd know all this

i looked at both routes and went for a xbox with 250 gig hard drive and will install the MC software as soon as it comes out of alpha