@Slimmegane:
You shouldn't need both a Rx and Tx cable. You are only going to be recieving data from the GPS aren't you? Or does it have some kind of programming feature to it? And where are you going to be putting it? I have my GPS tucked under the dash, and the computer in the trunk. This means I have something like a 6-7 meter cable running the length of the car. I just used a shielded headphone cable. One end has a DB-9 connection on it, with a short PS2 cable hanging out of it. You could just put a power connector on instead of the PS2 connection.
@Gutter:
Hey, I wasn't talking to you! Get back in your cage!