This is a short tutorial that will help you install a new league in FM 2012
First of all, after you’ve downloaded the league, if it’s a zip or rar, unzipit and place the “.xml” or “.dbc” file in the following folder:
My Documents/Sports Interactive/Football Manager 2011/editor data
If you don’t have this folder, just create it and and the file there.
Start a new game and play your custom league.
One more mention, the file you add are not compatible with any existing saved game.