You can also install from Tools > Extensions or by dragging and dropping the mmip file onto the Player.

Weird - I shut down the program and restarted it with no effect to get the skins installed as above problem. However, when I was messing around with it and put it into micro-player mode, then the dialog boxes showed up and I was able to install them. The skins are where they are supposed to be now.

I'm double-clicking the .mmip file and it opens Monkey and does nothing. The new skins are not there. Any suggestions?

Tools -> Options -> Scroll down to Skin and make your selection.

Full disclosure - I'm new to MM
I'm trying to install a skin extension, have downloaded it, double-clicked to install, even got the message saying it was successfully installed.
Problem is it isn't working - nothing at all changed.
I go to Tools, Extensions and both of the ones ive installed are listed and clicking or double-clicking on them does nothing.
It's almost like they need to be activated or something.
Can anyone help? Sorry for the most basic question.