sure someone can help I have moved/copy all the files related to iTunes Music library to my external HD and then set the pref of iTunes so that it recognise where to get the music and all infos from.
That being said you can notice at them bottom of this thread that other thread were posted about this subject and if not all listed then the search function in this forum should help you find the answer you're looking for.
Copy your iTunes library folder to the external drive. Open iTunes and select "Edit > Prefrences" and then click the "Advanced" tab. (Sorry, might not be exactly the same, running windows version of iTunes right now.) Change the "Library" folder to the iTunes folder on the external drive. Your iTunes library folder is in your "Music" folder. It's called "iTunes Music" i think.