Be sure and use Midknyte's link. The instructions at Arctic Silver are very thorough, and specific for different types of cpu.
If you use the shim idea, I'd be inclined to put a small piece of pvc electrical tape over that IC at the bottom to prevent any possible contact or shorting. The idea of the shim was to put more pressure on the heatsink for better contact and to help take heat out of the heatsink and thus the cpu. Good luck!
