If you simply want to edit the video, you may need Nandub instead. Most AVI's these days have VBR audio tracks and you can't work with those in VirtualDub. VirtualDUB only supports CBR audio.
I use both. I compress my AVI's with VirtualDUB, frameserve it with AVISynth, and manipulate audio with NanDUB.
http://ndub.sourceforge.net/
-S