Lat Long Coordinates System

I have a question about working with the coordinates system (and I hope I'm explaining this coherently). Basically, I need to make sure that I am properly calculating the exact distance between two Lat/Long points so that I can figure out the point that is exactly half way between the two points. First, I am converting to the decimal system to make the calculations easier. Therefore, the point (Lat N*41 52.0399