are you pressing f8 too late? bios loads before os, so it's probably user error
start mashing the f8 key once you turn the system on
pekv2 is correct. I mash before I even see the Asus logo menu, which clear shows "F8 - > Boot Menu"
Holding down ctrl indefinitely (right after booting up) works on every modern motherboard.
It just isn't very widely documented.
Give me a bit to try that. I need to do some stuff first. I'll post the results in less than half an hour.