There isn’t a lot that you can do. SoundTrackPro might be able to help it a little, but if you’re audio is clipped (from the mic source) that data is gone. It’s like overexposing video so you lose the highlights.
Try Soundtrack Pro or let an audio mixer listen to it and have him give you his opinion on it.
(without actually hearing it, there is only so much we can suggest.)
-Russ