I'm buying a GPS that uses SD cards as a form of memory for the software.. but I'm not sure if it is possible to change the software on my GPS to some other GPS software because I heard it is unreliable.

Does anyone know where I can download any GPS software or GPS hacks?
i have a MyGuide 3000
http://www.myguidegps.com/en/pro.php?p=11&pv=0