I have been a user of the XBOX Media Center since 2005 and it is a fantastic dashboard replacement and fully featured media center for the original XBOX. But since the original XBOX is no longer supported, the XBMC team decided to port the software to the PC and Apple OSX – which was about 2 years ago.
So what does this mean to you and me? Well, since XBMC is free and open-source, you can download it and install it on your computer. In short, XBMC turns your PC into a full fledged media center. Watch movies and DVDs, TV shows, listen to music, view family photos, and much much more. Here is what I use XBMC for: I set up a spare PC that has a TV-out port and connected it to my living room TV. I installed XBMC and linked up a few network shares to my PC at my desk. Using XBMC, I can stream media content from my desk PC directly to my home TV. Now the only thing I need is a Windows Media Center remote!
I highly suggest you check out XBMC on your own. Since it is free, what do you have to lose? There is a Live-CD\USB version of XBMC where you can boot to XBMC without needing to ever install it on a computer! Be sure to check out the screenshots at www.xbmc.org to see what it is capable of. Yes, there are plenty of other freeware\open-source media center software offerings out there but I enjoy XBMC much more than the others. Have fun!