Andreas Hegenberg, describing his handy Mac utility:
BetterTouchTool is a great, feature packed FREE app that allows you to configure many gestures for your Magic Mouse, Macbook Trackpad and Magic Trackpad. It also allows you to configure actions for keyboard shortcuts, normal mice and the Apple Remote. In addition to this it has an iOS companion App (BTT Remote) which can also be configured to control your Mac the way you want.
I have been using this free utility since I first got a Magic Mouse a few years ago. It is indispensable.