
With the help of the Automator programm "Fix DFU 10.5.6" users with Mac OS X 10.5.6 will be able to use the iPhone in DFU mode with iTunes. DFU mode is needed if you want to use PwnageTool or Quickpwn for the first time.
Mac OS X 10.5.6 was released on December 15th, 2008. It disables recognition of a device (like the iPhone) in DFU mode. It is not known if this is intentionally disabled by Apple or just a bug.
The Automator programm offers a one click solution to replace two plugin kexts with the ones from Mac OS X 10.5.5 and then rebuild the kextcache. After an automatic reboot DFU mode will be enabled at Mac OS X 10.5.6.
Read more about it here
http://www.hackint0sh.org/forum/showthread.php?p=374065