Sorry if these questions are stupid ...
It's not that they're stupid, they're just not part of the FCP universe. FCP is an Apple product based on Quicktime. Everything else is a hack, kluge, hassle, or just plain trouble.
If you must export to .avi, use a PC with a Windows encoding product like Microsftw WMV Encoder that creates your specific flavor of .avi. KNow that .avi is only an architecture, there are literally hundrds of incompatible codecs for the .avi system. Your client who is insisting on .avi has temproal issues, tell them this is the 21st Century.
bogiesan