You need VirtualDUB. Run it and load in your MPEG file.
Go to Audio Tab and select Full processing Mode. Click Audio tab again and select Compression. Tag MPEG Layer-3 and select 96kb/s 44.1 Stereo. Then OK.
Click Video tab and select Full Processing Mode if its not selected. Click on Compression and select DivX
MPEG4 Low-Motion, then OK.
Click on File and Save AVI. Done.
If you dont see the DivX
Low Motion in the Video Compression list, you will need to install the DivX Codec 3.11a. These are available form this sites DVD download section.