You could get yourself a program like autoroute and generate map images from it. You can use these with qpegps. you will also need to make a note of the GPS coordinates of the map end points while in AutoRoute.
Don't do it myself, but a friend I sold a Zaurus and GPS unit to uses it and is quite happy with it. Not exactly TomTom, but it works, and he is still my friend
As long as you don't distribute the maps to anyone else, then there is no problem.