As I posted in another thread here a couple of days ago, I am in the process of doing this and can probably do a write up as I go.
I am installing a mini itx pc and touchscreen system - I have all the hardware I need now I think, except some wiring and a 2003 satnav cubby, going to order that on tuesday when I am at the dealers...
I am thinking to visit a car audio shop to get some of the wiring done unless there is someone around sw london here who would be interested in helping out