iPhoto Library Manager stores the list of libraries it keeps track of in its preferences file, which is located at ~/Library/Preferences/com.mac.bwebster.iPhotoLibraryManager.plist.  If you copy that preference file to the same place on the new computer, that will bring the list of libraries over to the new machine.  You should quit iPLM on the new machine before copying the preference file into the Preferences folder. This will transfer your registration information over to the new computer as well.

Note, however, that the libraries will only be found on the new machine if the libraries themselves are located in the same place on the new machine.  For libraries on an external or networked drive, this should just work by connecting the drive in question to the new machine, since it will be showing up with the same drive name as before.  Any libraries that are stored on the internal drive of the old machine would have to be placed in the same location on the new machine in order to be automatically found.

If iPhoto Library Manager can't find a particular library, it will display its name in red in the library list, so that's a quick way of knowing which libraries it wasn't able to find.  If any libraries don't make the transition, you can just drag the library folder into the library list to add it back in.

See also:

Adding a library

Storing a library on an external drive

Copying a Library Between Computers