I haven't tried this (yet). However, one note that might be useful:
Note the heat sink compound on the tops of the CPU, video chip, and whatever the third chip is. You're going to need to clean that off the chips and the mating surface and carefully replace it with new compound. Mac's run hot, so it's important to do this carefully (for better heat conduction.
Buy a good quality thermal grease like "Arctic Silver" or "OCZ Freeze Extreme" (my favorite because its almost as good and easier to use). The instructions assume that you're putting the heat sink down on the CPU, but here you're putting the CPU down on the heat sink, so adjust accordingly.
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