I'll chime in. Stay away from OCZ. Now, PC3200 (AKA DDR400). Its just a math lesson. To run DDR400 speeds you need the right combo of FSB and mem ratio.
I'll use the new i845G chipset as an example.
150 FSB x 2 (DDR) = 300. 3:4 mem ratio = 300 x 1.333 = DDR400
160 FSB x 2 (DDR) = 320. 4:5 mem ration = 320 x 1.25 = DDR400