actually they are pretty easy, i installed Sirius into my dad's Monte Carlo. all you really have to do is run the wiring along the edge of the interior and under the trim thats along the edge of the carpet. on my dad's car he put the antenna module on the roof near the window and had the wiring run under the rubber seal around the rear glass and then into the trunk and then through the rear seats (which flip down). I personally would not go that crazy and have mine on the deck lid near the rear window
. I am not sure how XM is set up but on Sirius you don't actually hook it into the car stereo it has it's own antenna that connects from the tuner module and has a small wire that runs along where the dash meets the glass and then the antenna attaches along the outer side edge of the glass, then you just plug in the power cord into the cig lighter. if you want to have it done, it should NOT be that expensive if there are places that install car stereos, it should only take them no more than a half hour
.