The Windows 7 Media Centre now comes with an option to play your favourite music, which by default creates a changing list of songs based on your ratings, how often you play them, and when they were added (it's assumed you'll prefer songs you've added in the last 30 days). If this doesn't work then you can tweak how Media Centre decides what a "favourite" tune is- click Tasks > Settings > Music > Favourite Music and configure the program to suit your needs.