Compositing is simply taking the anmiation files created in Moho and turning them into video. I did this by simply exporting from Moho as high quality Quicktime DV. I was then able to import directly into iMovie. I could have opted to export a sequence of pictures such as jpeg files and compiled those in iMovie or the editir of my choice.
Here is a screen shot of my video being imported into iMovie.

iMovie now supports the import of most quicktime files. Older versions of iMovie are unable to do this. In the case of an older version of iMovie, you should import the Moho files as a jpeg sequence. If you import a sequence of pictures it is necessary to export you file to camera. Exporting to camera will turn the pictures into a video stream. You can then import the video stream and edit it as you would a video clip. By exporting from moho as Quicklime video, you bypass these steps and save time.