Using the script THENICEONE made - I did the install with OBMM
But when I try to activate Mart's Monster Mod 3.7 I get told that FCOM is not installed

What is the issue?

Did you install MMM before you did that? Because im pretty sure that needs to be installed before hand

You do have to install it first. Also I recall reading something in the install readme for 3.7 that states the changes in this MMM's update were done irregardless of it's compatibility with an FCOM install. Might be worth checking the readme again.

No issue really. It warns that you don't have FCOM, which you shouldn't when installing MMM, so it's OK.

Also, I'd recommend using the existing release threads rather than starting new ones. In this case: http://www.gamesas.com/index.php?/topic/995334-mmm-and-fcom-omod-installers/.