in the upper left corner of Garage Band (assuming you have the latest version) clink on the smart controls knob. in the new window that opens in the bottom expand the Plug-ins and then in the not so obvious grey area you can click on a spot to select EZDrummer after navigating through some sub menus. Very bad usability on Apple's part. I hope i explained it in a way that helps. I just now figured it out myself.
Don