I can get my midi keyboard to input to garageband but can't get it to play back through the keyboard. I'm using a midisport 2x2 interface connected to a usb port of my G4 ibook. Any help greatly appreciated Ooops! ......... just spotted that I have posted this in the wrong place, could a moderator move it please! Sorry! I've just read further and me thinks I may not be able to do this anyway, I await a reply from a more knowledgable person.
Garageband does not send midi data back to your keyboard, and thus, won't trigger your keyboard. For now, you can only play the instruments that are in Garageband. I think they were trying to keep the program as simple as possible for midi novices. Maybe a future version will include midi out/through.