Your motherboard, and CPU, will run with a "FSB" of 200MHz (400MHz effective) at stock. The only reason people tell you to by the DDR500, is because if you try to overclock your CPU (past 200MHz), the RAM will increase its speed to keep up. With DDR400, this means that you overclock the RAM as you overclock the CPU, something that not all RAM will like (and would sometimes force you to run a divider on it). But if you bought DDR500, it means you'd be able to overclock to a 250MHz FSB before the RAM even starts to be pushed past its design limits. So if you bought DDR500, and ran the CPU at stock speeds, the RAM would effectively be underclocked back to DDR400. DDR500 will run fine in your mobo, to answer your question. Sorry, I'm tired, so I apologise if my explanation was a bit erratic and confusing.