It is just some LED light. There are a few thread on this as well as the General Discussion Forum, take a look and see if you have specific question.
The good news is that LED moonlight is one of the easiest DIY project there is. It is usually cheaper (if you can wait) to order the LED online than drive over to Radio Shack.
Like Tangir1 said, its an easy DIY project. I think the rope light idea is even easier though. I have 2 blue LEDs being used as my moonlight. They give off a nice shimmer on the water since they point source. You can see some pics of it if you do a search in this forum for LED.
The Outer Orbit Fixture by Current and the Coralife HQI Pro fixture both use something similiar to 1W LEDs for moonlight. Check out www.theledlight.com. I bought (3) 1W Luxeon star LEDs for my 125 and am happy with the results.....