A useful tool is VirtualDub. You can find links to it with a dogpile or
google search or find it in the tools section of videohelp.com.
I use virtualdub to remove audio as wav (edit audio in another app), strip
audio from an avi (import video in Animation:Master for rotoscope), or
convert a misbehaving avi file for an import into my editor. It has a lot
of uses.