Well, I didn't try downloading it, so I don't know how many megs (or gigs) this file might be, or what size you are looking to convert it to. But there are a ton of free programs designed to convert mpeg to a divx avi file, which should probably only be a few megs, since that segment was only about 20 minutes. I've downloaded 20 minute movies that were about 100 - 125 megs, so that is a file size you should shoot for.
Anyway, there are way too many to list, but I would recommend checking out VideoHelp.com
and just use their directory to find a program that suits your needs. There are also plenty of great guides there for most of these tools that will give you step by step directions on how to convert your file.