I have recently purchased a Toshiba e570 PDA, and would like to buy the additional hardware and software to give myself a GPS system. I'm a coach driver so the ability to shift it between vehicles is important. I've got myself totally confused about what kit I need to purchase. I've seen some big card things on ebay

with big lumpy bits

on the top marketed as GPS recievers, others referred to as Bluetooth, for which I assume I would need a Bluetooth card? Some cabled solutions, some wireless solutions.....
I'm technically minded, but new to the PDA world. Thought it would make my life so much easier though!
For the record, I've seem a demo of the TOMTOM navigation software which seems to be good, so I'm tempted towards that, but having said that, I haven't seen a demo of the other packages. I'm most confused so any advice to point me in the right direction, or to advise on the total package I should buy, will be very much appreciated!
Mark