GPS feed to PDA

Rightly or wrongly, I have a Road Angel GATSO finder in my car. Having become recently old and boring, I don't need to detect speed cameras, but the Road Angel has a GPS output socket. I imagine this GPS output could be used to give me a routeplanner thingy in my car,via a PDA, on the cheap.

Does anyone know what hardware/software I would need to buy? All the packages I've seen (in PC World) seem to include (at considerable cost) the actual GPS receiver, which I'm guessing I wouldn't need. The young lad, in the shop had no idea.