You remove the black heatsink bracket that surrounds the CPU socket, which reveals the two mounting holes for XP64 on either side of the socket. The block is mounted by screwing a pair of 6-32 threaded bolts into the mounting back-plate that should have come with your motherboard.
With the first batch of Storm blocks I included some 1.5" long 6-32 bolts to do this, but hadn't realised that not all mobo makers were not following the AMD reference back-plate design, and that some XP64 mobos (DFI included) require 2" long 6-32 bolts to mount the block properly. I have been shipping the 2" long 6-32 bolts for free to anyone who asks who has a Storm block, and the 2" long bolts will be included with all future blocks.