Thanks mate. I'll keep everyone informed (actually more like I'd be begging for help )
Co-Pilot is expensive (my IPAQ 4150 and Bluetooth GPS) cost the same as the software does on its own! But my main reason for wanting a Car PC (besides being cool) is the customisable Sat Nav so hopefully it is worth it.
The main problem with the IS regarding a CarPC is the age old Aux-in input issue. I have tried a Tape Adapter (hated it wurring around - got annoying), FM Transmiter and Modulator and they were all poor. Gordon has an FM Modulator in his car that he said works well - so I might give that ago!
I don't really want to replace the Head Unit (I like it, and it will be expensive), so I will continue to investigate. I have read in the knowledge section of this site that you can add RCA inputs by doing soldering and cutting some wires - but I'm not really confident enough to try that!
Thanks