Thanks for the link. Actually, it isn't quite what I'm looking for.
I'd like to use my PDA navigation off road and for cycling. The problem is that the tom-tom software that I have is specific to car drving. It doesn't allow all of the roads that bikes can use, sometimes plans a route on a motorway or other non-suitable road and doesn't work at all off-road.
At the moment, it looks like I'm going to have to buy a Garmin or Magellan device but I'd thought about saving cost by using the GPS that I have on the bike.