I got a message there was insufficient room on my harddrive to download a movie rental from iStore. I discovered my Applications folder had duplicated itself 32 times. I went to the the last duplicated folder and deleted it. Then discovered I had deleted all my applications Now I'm trying to copy my applications from an external harddrive to the Mac, and am told there is insufficent space on the harddrive.

1. what happened?
2. how do I fix it?
3. how do I stop the duplication happening again?