Well, I don't think you're ever going to get crystal clear audio out of that, but there are some tools that can help.
Audacity -- http://audacity.sourceforge.net/
-- is free, and has some editing filters and features, like "denoise," that could help.
Personally, I use a commercial product to clean up audio -- DC7 from Diamond Cut Productions. It's pretty expensive -- it would do a better job than Audacity, but probably not that
I'd start with Audacity and see how it works.
Try denoising it first, then increase the gain.
EDIT: I should point out that both Audacity and DC7 are audio
programs. You can't clean up the audio track of a video with them unless you can separate it out from the video, clean it up, then combine it again. So, on second thought, these might not help you after all. Sorry.
Edited by Capn Easy, 05 July 2009 - 01:17 AM.