as days pass by

Loads of people are starting to get GPS stuff in their cars. I really want this, but I don’t want to pay a lot. Aldi were doing a thing that was a GPS receiver and a PocketPC, so you could use the PDA as a PDA and then plug it in when you were in the car to have it do GPS —it spoke to you and told you where to turn and so on.
I think this should be doable with a Zaurus. You can buy CompactFlash GPS cards, which will plug into the Z, so that would work fine. What’s missing, however, is the map data. It seems that there isn’t any freely available vector map data which a navigation program could use. Damn. (You need vector data, not bitmap data (pictures of maps) because in vector data the points where streets meet and so on are identified. Computers can’t do a lot with bitmap data other than display it; they can’t interpret it.)
I wouldn’t mind the idea of buying some map data, if that were possible. Has anyone done anything like this?