I have the regular P4B266 so I can tell you how the problem works for me. If I O/C to 133 MHz FSB (and I think any FSB over 100 MHz) the light in my optical mouse flashes non-stop before it posts, and it freezes before booting. If I plug the mouse in any of the USB 2.0 ports then it boots fine (even @ 133 MHz FSB where the CPU is massively overclocked).
So, to test the problem, try overclocking your CPU by setting the FSB to 133 MHz and see if you can boot (if you have a USB mouse). If the computer boots, then you don't appear to have the problem.
I'm not sure if its just mice or any devices (I assume it's anything) in the USB ports, and I don't know if there's any fixes yet (a new BIOS from Asus could maybe help).