Originally Posted by phobus

You can easily check if it's the chainring or crank that's out of round. Hold a straight-edge or something against the seat tube, parallel to the ground, so that it sits just above the chainring. Spin it around by hand. If the gap between the straight-edge and teeth changes as it turns, it's not round. At that point you can remove the ring, and repeat the test against the crank itself, to see if the five holes are

I'd do this before spending any money at all, since the problem could be the ring, the crank, both, or something else entirely.