Download a programme called 'VirtualDub'

It's very easy to use, if you have trouble though I can guide you through the process.
Or I'll do it now...
1. Open up the programme and open the file you wish to compress.
2. Go to 'video' and press 'full processing mode'.
3. Go to 'video' and choose 'compression'. Pick the codec (Xvid or DivX).
4. Then go to 'audio' and press 'full processing mode'.
5. Go to 'audio' again and choose the codec. Pick MP3 in the window on the left. In the window on the right choose 44100hz and 128-192kbit/s.
6. Click F7 to save file in specified destination.
If something is still unclear feel free to ask
_FleischmanN_