If you get a wiring harness and change that and the center console harness it would all be plug and play, however it is a considerable job and if you have base sound package finding a hud harness with base sound and not monsoon would be difficult, however the wiring is relativly simple, switch goes directly to the heads up display, then you got a positive and negative and one data wire which you splice into the ones going to the speedometer would not be hard to do at all, then its just a matter of carefully cutting the dash to accomodate the hud and new trim bezel.
Here is a nice write up
Grand Prixs Of North America • View topic - 04+ GP HUD install for Dummies*WARNING-PIC HEAVY*
When I get the parts I will be doing it myself and will probably remove the whole dash so I dont damage my windshield or anything else.
I already got the wiring in my car since I swapped the complete interior wiring harness with another from an 04 with all the options plus modified it for dual climate controls.
