HI guys, I use the Compaq iPaq, with the Rikaline hardwired GPS and Tomtom 2 software, and had no really problems. If you install it cleverly and use the Aux input into the Stereo, you can use the ipaq has an Mp3 player, whilst the sat nav is running and directing through the Mini sound system.
If you already have an iPaq, pick up the Rikaline GPS equipment from ebay - priced around £70. ( If your lucky you'll get the mount and power cables as well!) - Working in the IT Industry, i can get a copy

of the Tomtom 2, CoPilot 3 or any games / applications, supplied with all the relevant details to allow them to work. PM me if anyone's interested.