I’m running Win7. When I installed ActivePerl I also got an app called Perl Package Manager.
I install OSM2MP.pl in the same folder as the OSM file I want to convert.
As you run OSM2MP you will get a series of error messages identifying missing library components. Browse for them with Perl Package Manager and install them. It may take a few tries, but eventually you will find all the packages you need.
It might be easier to open OSM2MP.pl in a text editor use the Package Manager to find the “required packages” listed at the start of the file.