The easy fix is a program called Terrabits (Terabits? Don't remember) Avi Editor.
Terabits will let you make micro-scale changes to your AVI's framerate, which can fix those silly audio problems. I drop a couple of frames in every hour of cap, and usually have to make a micro-change from 29.997 fps to something like 29.9965 fps.
Of course, that doesn't work if you're dealing with an MPEG or you're wanting to convert to a VCD. There are other ways to fix the problem in that case, but they're complicated and time consuming, which is why I cap MPEG destined to become .AVI files.