DDR400 is the only one I know of, you will have to set it in your bios to match the FSB of your CPU. I assume it would be 333mhz, bios setting should be 166.
I did a goole search and only came up with some forum questions and found nothing on the Asus site. Does your manual say anything at all.
This is only a guess, and more the info you can give might help too, system specs ect. Anything showing what you have now. Stickers on the memory chip.