I just installed an XM receiver and head unit (Pioneer) in my '03 Expedition and have to say it was a breeze.
I put XM in my other car and quickly learned I can't live without it.
The dash piece is held on by two screws. Then it just pops off exposing the factory radio. The radio is attached with two screws and when removed, the unit comes right out. Now the neat part. There's a ton of room in the radio area so I was able to stick the XM receiver in that area eliminating the need to run wires under carpet, etc. There's also room to stick an amp. in there if I decide to update the speakers. Now, part two of the neat part. I bought a new XM antenna made by Sony which is much smaller than the Terk, and rather than stick it on the roof, I decided to try it out on the inside where the dash meets the windshield. I ran the antenna lead through an existing slot in the dash to the XM receiver. Thus far, the antenna works great in that location.
Other than the time to wire new matching connectors to the head unit which I did at my desk, the installation is a 15 minute job. 30 minutes max.

 

Do you have any pics of the install???

 

No. But it's a straight up job. Nothing difficult at all.