I'm not the brand manager for Windows Media Center, but I did what Jackie Huba said to do anyway and found this: http://www.youtube.com/watch?v=rQKI7YvtLhQ&search=Media%20Center at the top of the search results for 'Media Center'. Pretty cool romp through our user experience.
Update: These are still kinda lame (especially compared to iPod + iTunes commercials) and don't actually speak to what Windows Media Center is all about, but better than the general 'Start Something' campaign.
http://www.youtube.com/watch?v=8NDSKAa4WMI&search=Media%20Center
http://www.youtube.com/watch?v=ve1OEey8ryA&search=Media%20Center
I'm beginning to see why awareness of Windows Media Center is pretty low, if these commercials are 'the best we could do'.
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.