Well here are two pictures of a Noctua NH-U12P on the Asus P6T from thinkcomputers
The dimensions of the Noctua NH-U12P, according to http://www.thinkcomputers.org/old/index.php?x=reviews&id=926
are 158mm x 126mm x 95mm (HxWxD), with 47mm of clearance.
The dimensions of the Zalman CNPS10X Extreme, according to frostytech
are 161x131x100mm, with 37mm of clearance. So if I'm right the fan would only extend 5mm further over the dimm slots. So aslong as you don't need to use the black slots it will be fine. If you did need to use them, then I would think that aslong as the RAM was installed without the fan attached then it could be done easily enough.
But then I suppose that could bring doubt over whether the capacitors would then get in the way of the Zalman. Which I can't answer from the research I've done so far.