when you plug in to the isp header does the rainbowduinos red light come on?
When i was hooking it up the first time, it felt like it was backwards on mine, like it was meant to have the header pointing down not up but i could be remembering wrong.
I dont have it in front of me know, but maybe tonight i can look at the wiring (if its still hooked up) or find a picture of how i had it.
you should be able to find the ground and power pins pretty easy, they make the red power led come on. after that, adjust your orientation of the other cables.