sleep timer for line-in?

[lemmiwinks]

I currently have a external XM radio that I run into my computer through the line-in input on my sound card. I'd like to listen to XM when I fall asleep. The essence of my question: is there some sort of software/media player that can monitor line-in and basically assign a sleep timer to it?

 

[DarkTXKnight]

What about using citrus alarm clock to time it?

http://www.ornj.net/citrus/

Ive never used it but always heard good things about it