You need to download the script file from this page (just follow the instructions given above), and then place it in the users' Gimp scripts directory (so you can upgrade Gimp without loosing the script). In order to use the script, you need Gimp 2.6 at least (2.8 has just been released, but I haven't tested it I you do, please drop me a message).
Some notes about setting up and using the script with Gimp
