Have monsters appear in places where they usually don't?

I want to turn the Crescent mountain cave into a mini-dungeon of sorts, and of course that means I need to place monsters in there. How would I assign it to have a certain pack of monsters appear there, if the place is usually devoid of monsters? Is it done on usME, LE or something else?

I think you can do this in the LE. In order to actually create the packs you'd need the ME though.