Windows Media Center
You should also check out Windows Media Center. I have a Media Center PC with over 500gigs of storage and all my songs are compressed using Windows Lossless compression. I stream all the data to my XBox 360 (you can also use a regular Xbox with the Media Center Extender disk). The user interface is fantastic and the 360 outputs audio over a digital optical link and video in 720p over component connections to my receiver (Yamaha RXV-2600).
I also use if for all my pictures and standard def TV. Unfortunatly, Windows Media Center will not support Cable Card (HD over Cable) until Vista is released at the end of the year. I just use my cable box for HD TV right now.