I just started C25K yesterday... I still don't know how a few weeks of warm-up and preparation could possibly get me to run 5K/3 miles without stopping, but perhaps running is all about the gradual build-up.
However, since I have had a few brief run-ins with running, I CAN say that pushing yourself too hard (I would run forever once, even AFTER everything hurt, just to lose more weight) will make EVERYTHING hurt! Side pains, thigh pains, calf pains, charliehorses, you name it - running seems to be one of the most physically taxing exercises and unconquerable battles