Don't trust small jumper cables. Thicker cables transfer power much better than the flimsy ones you might have in your car. Also, if you don't have a pair, I'd say that the longer the better.
Example: I tried jumping a friends car tonight with his small cables and after 15 min of nothing really happening I ran into the nearby store and bought some monster cables. They were long enough to circle around about 40 cars, which was great because I didn't feel like driving over to the other side of the parking lot where his car was. In about 5 minutes we were in business.