When you click on the "Save as AVI" button what happens? Doe's it at least give you a list of codecs to choose from? Try and describe for me what isn't working. If you are using the default "Full Frames (uncompressed)" it will take quite a while, and the file would be quite large. Best bet is to take a short piece of film and try exporting it with some of the different codecs listed and see what gives you the best results. For me the best one is the "XviD Mpeg-4" codec.
You can download a free version of FRAPS from here.
http://www.fraps.com/ It works super easy with the film viewer but the free version limits you to 30 seconds of recording at a time, and watermarks everything with FRAPS.