Personally I think video editing is one of those areas where, like Moho itself, it's worth spending 100 bucks, even if you're a hobbyist.
Worth investigating, for Windows:
Sony's
Vegas Movie Studio 6 US$90
Serif's
MoviePlus 5 US$80
Pure Motion's
EditStudio 5 Home version - US$75, Pro version US$150
As far as I know, this one doesn't handle Moho's alpha channel, so you'd have to use chromakeying for compositing.
rpc9943, as Moho doesn't export MPEG files, either the problem is in the AVI file or in the conversion tool you use to create MPEG.
Note that even if the AVI file is in perfect synch, it may not play back in synch if the media player you use can't keep up (or possibly your CPU is too slow).
I've heard
VideoLAN VLC media player is a good media player to try if the problem is in the playback rather than the file.
A decent video editor may help with sound synch problems, whether you need to resize one of the tracks (audio or video), slip the audio track sideways a liitle, or even break up the audio track into separat ebits and re-align the bits. Some video editors can do a little automatic resynching in some cases.
Note: videocaptured MPEG synch (usually due to dropped frames) is a different problem from rendered synch problems.
Regards, Myles.