GPRS coding to calculate distance and time

Question

I wish to make a system which will be used for medical purposes. this system will be reading the GPRS co-ordinates of the patient who logs in (by phone or computer) and calculate the distance from the nearest hospital (hospital co-ordinates will be pre-provided) and advice him/her the time they can use while walking/riding/driving. the problem is that i don't know where to start. please advice and if possible give out some links to appropriate tutorials or codes.