The main differance is passing and ball handling. Your prototypical PF will have a little better BH and lower passing and some outside shot, think Karl Malone working the post. Most C's will have bad BH and decent passing, catch and shoot or pass it in and out of the paint.
SG and PG. SG's will generally have better PE, with slight less passing than PG's, but honestly a good SG can play the 1 as can a good PG play the 2. Your PG is generally going to be the fastest guy with the best BH and PA, or the best option combining those three.