I happen to own a Sirius SL100 portable satellite radio. The unit itself has a built in satellite antenna, so I don't need to worry about the antenna part of the solution. I just need to be able to pass the audio via the headphone jack into the PC which in turn sends it through the car speakers using my amp.

In my testing using a laptop I was unable to use the headphone jack from the SL100 into the laptop headphone jack. Are the headphone jacks of most devices basically a line in/out jack? Does this even seem plausible to use satellite radio via my pc?