I won't lie to you -- it's going to be a steep learning curve to learn Media Center Markup Language. But the payoff is quite nice, given the fact you can create experiences every bit as nice as Windows Media Center itself.

Some links...

SDK: http://msdn2.microsoft.com/en-us/library/aa286546.aspx
Discussion: http://discuss.mediacentersandbox.com
Team Blog: http://blog.mediacentersandbox.com

Charlie