The Noctua NH-U12-DX 1366 is an aftermarket CPU cooler for LGA1366 Xeon CPUs.
On Noctua's site they state:
Caution: The NH-U12DX 1366 can only be used on mainboards that have a backplate with screw threads for CPU cooler installation (such as the Intel reference backplate for Xeon 5500). The cooler is thus incompatible with Xeon 3500 and Core i7 mainboards that don’t have such a backplate.
How do I know if the Asus P6T has this backplate?