Windows XP Pro used for Media Center PC suggestions?

Hello - I do not have a license for Media Center but I have built a XP pro machine for use as a media center server. I don't believe you can download the Microsoft media center application as a stand alone install so I was looking for suggestions for other programs out there that essentially do the same thing.

System specs:

We should start with the announcement that this is a micro ATX pc in a "cute little box" (quote from girlfriend).

CPU: Intel 478 P4 3.2 GHz
Mobo: BIOSTAR P4M80-M4 Socket 478 VIA P4M800 Micro ATX
Memory: 2 x 1 gig strips of whatever homeless 184 pin memory I had laying about...
Video: ATI Radeon 9800 Pro
Sound: Turtle Beach Montego
TV card: um yeah... probably should have written that down. Winmax? Not sure. It's got coax video, coax FM, and and s-video outputs