I'm running a 512M stick of DDR400 (or PC3200, same thing, different way of saying it) in the shuttle box I built for my girlfriend that's using an AMD AthlonXP 2500+ Barton core that uses a 333Mhz FSB and thus requires DDR333 or PC2700. I believe the price difference between the DDR400 and DDR333 was $3 and the faster memory would theoretically give me headroom to overclock the system but it's actually pretty speedy and more than sufficent for what she uses it for so it still runs stock clock.