http://devnull.sweetdanger.net/fcominstall.html says:
- Download MMM 3.5.5 OMOD or FULL package extract the 'Meshes,' Sound,' and 'Textures' folders into your "Data" folder. Do NOT use any of the ESMs/ESPs from this version!
- Download MMM 3.7 BETA and extract the 'Meshes,' Sound,' and 'Textures' folders into your "Data" folder (overwrite, if necessary) together with Mart's Monster Mod.esm
- At this point, you should have only ONE plugin from MMM installed - Mart's Monster Mod.esm
The download links actually instruct you to download MMM373BSA and MMM_37b3_Public_Release. MMM373BSA extracts to just a single file called MMM.bsa while MMM_37b3_Public_Release extracts either .ESP or .ESM files and no folders.
So what are you meant to do at this step?
Cheers
Bezerker