BandToLogic

BandToLogic is a tool to extract the Logic song data out of GarageBand bundles. Open a GarageBand file in BandToLogic and it will create a Logic song file for you in the same directory.
Please make sure you read the warnings section on the product homepage, the generated song file underlies serious limitations.

However, it should help you to easily export MIDI and audio data from GarageBand songs. Requirements
PPC, Mac OS X 10.3 or later, CamelBones framework (see product homepage).