Ummmmm... free sirius?

Okay, so I bought a used Jeep Grand Cherokee in '09. The dealer said nothing about satellite radio. Last year on a long road trip my friend started tuning the radio and must have hit a few buttons I never really messed with and suddenly we're listening to Howard Stern. Since then I have been trying to find the EIN number or code but no luck. The channel only goes as low as 2 and and high as 184. (not all channels are available) My question is how do I find the code or should I just sit back and enjoy the freebie?

What I'm curious about is if I can use this code for my computer too.

I had the same problem with a recent used car purchase. The dealer found the radio id # via the vin # of the car. Sirius would not recognize the vin # as having the radio; but finally accepted the id #. Still looking for owner's manual for the radio though. Their chat line people and "special tech" people are not too bright and only read answers from their prepared scripts.