I just purchased a pair of 1GB PC3200s and the system keeps coming up at 333. Doesn't matter which slot 1 & 2, or 1 & 3, even though page 2-12 explicitly lists that either doublesided or singlesided DDR can be plugged into 1 & 2 and achieve 400.
I'll bet you have a HW Rev 1.04 board (not to be confused with BIOS rev), like the rest of us early adopter suckers. There have been a number of problems with the 1.04 HW rev. First, I learn that OC'ing abilities are extermely limited compared to the 1.05 HW rev. There their in the memory voltage limits only on the 1.04. Then my NIC dies.
Then yesterday I remove my 3 512 DDR and install my recently purchased 2 1GB DDR. You see, the manual says that 3 will run at 333, and 2 will run at 400. I wanted more and faster. But not on the 1.04 HW rev. Asus can't even build a product to follow their own manual.
http://www.xtremesystems.org/forums/archive/index.php/t-44867.html. The thread begins with this very text, "Right, decided to start another thread for this motherboard as the old one was basically about how bad it was." And that thread opened up on 08-16-2004.
I've never been so disappointed with an Asus board as I am with this one. Not many people got the 1.04 PCB.
I'm sure that Asus thanks you for being a good sport and buying their fine board.