If you click just once on each of the libraries you can see where they are located just below the window:
If you find that the libraries contain photos you want to keep you can use the paid version of iPhoto Library Manager to copy the two smaller libraries into the larger one.
If all of the entries are pointing to the same library then there may be preference file damage. Make a temporary, backup copy (if you don't already have a backup copy) of the library and try the following:
1 - delete the iPhoto preference file, com.apple.iPhoto.plist, that resides in your
2 - delete iPhoto's cache file, Cache.db, that is located in your
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3 - launch iPhoto and try again.
NOTE: If you're moved your library from its default location in your Home/Pictures folder you will have to point iPhoto to its new location when you next open iPhoto by holding down the Option key when launching iPhoto. You'll also have to reset the iPhoto's various preferences.
NOTE 2: In Lion and Mountain Lion the Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and hit the Enter button - 10.7: Un-hide the User Library folder.