If you started with a highly compressed QuickTime file (mov) and created a gently or uncompressed AVI, then yes, that's exactly what you get. That's what happens to us when we need to cross a Mac file into one of the PCs. That's one of the ways to do it.
So you have to dig a little deeper. What kind of Quicktime file did you start with and what's the internal compresser that you're using inside AVI?
QuickTime Player INFO would be a good place to start. (Apple-I while QuickTime is running)
If you're using an H.264 Quicktime and try to create a fully compressed Windows Media file, it's likely little or nothing will happen since they both use similar technologies.
Lest you get really cozy with your QuickTime movies, remember that uncompressed, undamaged NTSC (American Video) is about one meg
per frame (30 frames per second, sixty seconds per minute.....)
Koz