Firstly an .avi is a container file, and divx is a codec.
I use a program called virtualdub for my converting needs. It's stable and free. Depending on the file you are wanting to convert, you may need to download plugins for it. .wmv and .mp4 both need plugins to be read by virtualdub. But .mpeg and others can be read and converted as is. Also, I vastly prefer the xvid codec over the .divx, an I would suggest downloading the xvid codec and using that as your compression filter.