are you going in dash or a portable unit?
I have a portable unit that I use in the car and on the PC and in a boombox.
Its a bit of a hassle as sometimes I forget to bring it with me. But Sirius charges you extra to have more than one device (car and home) so you don't have to lug around yet another gadget.
I bought a universal Satellite mount that I drilled to the inside of the cubby hole below the radio. I had a local speed shop do the hardwiring and the antenna was placed in the car corner of passenger dash.
Satellite radio is the greates thing. Everytime I forget to bring it with me into the car I'm reminded how bad FM radio sucks.