I pulled the stock head unit out of my 02 GT last night. First you have to remove the plastic trim that is around the gear selector. Pull the trim up and out away from the dash area. You will need to disconnect the 12 V accesory socket at this point too, so you may want to disconnect your battery just to be safe.
Next you need to pull the dash trim from around the radio, temp controls and two vents. Note, the two vents will be removed with the plastic trim. You will have to disconnect the three switches at the bottom of this trim panel too. The left plug will be orange/brownish, the middle is grey, and the right one is purple(if you have these). Once the plugs are removed, you need to work the trim away from the dash board and it should pop off with some motivation.
Once that trim is removed, there are two screws at the base of the radio trim that needs to be removed. After those are removed, the radio should slide right out.
Good luck wiring in a new head unit, I'm having troubles with that right now.