I am new to this Nokia 770. What I have tried from yesterday is to install Meamo Mapper(do not forget to install Flite to get audio guidance), which is free and buy a i-blue gps receiver, which cost around 60$ (which is the only cost). That's all for a nice GPS setup.
I have not fully test it since I am at work today, so I cannot give you the comparition with a full blown gps sets.