iTunes 10 for Mac: Import music and video already on your computer
Here are ways to add items from your computer to your iTunes library:
Drag a file or folder from the Finder to the iTunes window.
If you add a folder, all the files it contains are added to your library.
In iTunes, choose File > “Add to Library,” locate a file or folder, and then click Choose.
By default, iTunes places a copy of each audio file in the iTunes folder (Home/Music); the original file remains in the current location. For information about adding an alias to the file (instead of creating a copy), see Add items to your library without copying them to your iTunes folder.