For the pin mod in notebook computers (I'm assuming your referring to for the P-M's and celeron M's) the logic is this. We knew there is a chipset that supports both 400 fsb and 533 fsb, and processors that run at either of these speeds. The processor has to tell the motherboard what kind of variant it is (400 or 533) so it communicates this through a couple pins bsel1 and bsel0 I believe. To figure out what pins communicated the speed you could look to intels white sheets which defines what every pin is for, and from there you just have to figure out how to make the 400 fsb variant look like a 533 fsb variant to the mobo, in this case by grounding bsel1 I think. I did not figure this out originally it was some1 else, however I did figure out the same kind of mod for my P4 630 in a dell 8400 which allows me to run it at 4 ghz.
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