Currently Being ModeratedNov 28, 2012 9:39 AM (in response to vincefiorilli)
Copy your ENTIRE iTunes FOLDER to the External Drive...
Full Details Here > http://support.apple.com/kb/HT1751
Currently Being ModeratedNov 28, 2012 9:43 AM (in response to vincefiorilli)
Most likely the drive is formatted NTFS which Mac OS does not write to.
I suggest you simply reformat it (Mac OS Extended, Journaled) and enable Time Machine (rather than copying only the iTunes folder).
See this -> Mac Basics: Time Machine