How to create an uncompressed AVI from FCP inside:
1. Get the footage you want exported into its own sequence.
2. Export> QT Conversion
3. Choose QT movie as your format and go to settings.
4. Select None as your compression and make sure the settings are the best that you can get them.
5. Save the movie and open it up in QT.
6. File>Export
7. Choose Movie to AVI
8. Under Options>Settings, select None as your Compression and as before select the best settings.
9. Name it and save it.
This worked for me and I hoped it worked for you. It may vary depending on your footage but I think that the general principle is the same.
G5, Mac OS X (10.4.7)