Dont go with Sirrius, It is inferior to
www.xmradio.com and is rumored to file bankruptcy. XM radio is a different technology where you receive the signal directly from the satellite and has true nationwide coverage whereas Sirrius relies on a serious of transponders on the ground to deliver the signal.
XM also has better programming, most of which is commercial free.
Check out there site to see all the different units you can buy.
Definately the best gadget I ever bought.