I have one on order and would like to put a water block on the northbridge (there's currently a big passive cooler, but I'm guessing that this would need airflow from the CPU heatsink fan - which I've eliminated).
I very much doubt that it needs any extra cooling. Do you have any case fans? How about the PS fan? They would have put a fan on it if they thought that it even remotely needed it. No, I'd count your blessings that you have one less thing to worry about. The nForce and nForce2 northbridges run relatively cool, and you will have an excellent motherboard -- that runs silently all on it's own.
Save your cooling capacity (and it's fan noise) for the CPU and maybe a honkin' video card!