Once you have the basic hardware, just add a bit of software and you get a HTPC you can remote control and use from the couch comfortably.
http://mediaportal.sourceforge.net is a software package you can install on top of Windows XP and use that to play about any media you want. It has support for, among other remotes, the Windows Media Center remote so add that and you're good to go.
If you want to expand on your HTPC usability, add in some TV cards from the cards that Mediaportal supports and you can use your HTPC to view, timeshift and record TV too.
There are other HTPC software packages too, of course, I just like Mediaportal.