how do I shave about 20 megs off an Avi file?

[Endless Summer]

So I can fit it onto a 700mb CD?

[benderman]

Set video- and audiobitrate to 0 kbps, that will save many many MBs.

[DivZ]

remove the end credits with virtual dub.

load your avi, find where the credis start with the slide bar.
set your start and end points to omit the credits
set video to direct stream copy and audio to direct stream copy
and save as avi

[Enchanter]

You can also extract the audio track and reencode it at a lower bitrate.