This is probably old news, but you can buy the XMD1000 ($50) which is currently the heart of their after-market automobile system, Then make a cable which connects this device to your PC ($15) and 12v power. Using software, you can timeshift the music. Complete kits can be bought from timetraxtech.com. :)
Audiophiles beware, this relies on a digital to analog conversion in the XM device, and then a analog to digital conversion in the PC. The music sounds good to an undiscriminating listener like me, but is probably not a great choice for creating a music library. :( I like listening to the music at my PC without burdening my connection to the WWW.