the PC2700 runs at 333MHz, it's DDR (Double Data Rate) so the 166 is only half the equation..... If you're CPU's FSB is 200 then it'd be more efficient to go with the PC3200 ram otherwise you'd just have a bottleneck in your system......If he's got a 200FSB CPU then I'd say go with the PC3200 because he can only buy more later. If his processor doesn't have the 200FSB then well I'd still go with PC3200 because if he ever wants to upgrade his processor the RAM is already taken care of and again he could always buy the other half of the memory later. We're talkin speed vs quantity almost...I couldn't tell you what kind of comparison is between a gig of PC2700 and just 512 of PC3200, but for upgrade reasons down the road I'd say go for the PC3200.