iTunes keeps duplicating songs

Whenever I import mp3s from some location on my computer that isn't in the library, iTunes creates a copy of these songs in my library.

I only have a 10 gig drive, and this kills my disk space. Is there a way to set iTunes to move the songs, rather than copy them? I've looked through the preferences, and I haven't found anything.

iTunes Preferences, Advanced, General and uncheck "Copy Files to iTunes Music Folder" and it will stop duping them.