Hmmm. I think i have this straight now. I just asked a few of ya privately about this... thanks for the help.
Basically, i'm limited by what the fsb of the mainboard is. If i've got a mainboard that operates at max 400fsb, i can toss in a chip that's operating at 266fsb and a memory module that's 333 with no problems. The same would be true if i had a processor that was going at 333fsb and i stuck a memory module that operated at 266 (although, as some of you say, i'd have bottlenecking).