Hereafter is a report from Clément:
Garageband (08 or 09) was not working properly in on PowerMac G5 Quad after Mac OS X 10.5.6: very slow almost frozen system, audio/midi preferences not available, only 2 seconds of recording or playback. Making a clean install of Leopard and Garageband does not help, neither repairing rights on HDs, files or folders, deleting prefs files etc. All PM G5 owners were complaining as illustrated in this post: http://discussions.apple.com/thread.jspa?threadID=1788989&start=0&tstart=0
Till this message: http://discussions.apple.com/thread.jspa?messageID=9734914?