Usually when you get audio with no video it’s becasue your computer doesn’t have the Video codec needed to display the video. A codec is a Compressor/Decompressor and is the software that compresses your video while recording and decompresses it to display again. What you need to do is figure out what codec you need and install it.
Google for a free utility called GSpot and install it. Open the AVI file with GSpot and it will tell you what codec the file needs. Then google for the codec and install that.
WARNING: I would strongly advise against installing a “codec pack”! These are where people group a bunch of codecs together so that you have every codec imaginable. This is only a good idea on a media server where you just want everything to play. For a video editor, it may actually replace some codecs that you already have with inferior ones and give you worse video quality or replace them with decompressors only and disable your ability to write files in that format. Some of these codec packs contain viruses and Trojans that take over your computer. Just stay away from them. You’ve been warned.
~jr
http://www.johnrofrano.com
http://www.vasst.com