How to transfer music from one iTunes Library to another on the same computer?
The easiest way is to create a folder, say on the Desktop, then open that folder. In iTunes, create a playlist, and add all the music you want there. Select all these items, then drag them to the window you opened for the folder on the Desktop; the Finder will copy the music files. Next, quit iTunes, launch it and choose the second library, and add the files by dragging them onto the iTunes window. You can then go back and delete the files in the original library, if you want.