Yeah its kind of stupid that Asus put that PCI clock setting in bios because it has never worked in any of the bios on my board. It does not lock the PCI bus! Test it with Clockgen if you don't beleive.
Since the beginning 1 thing and 1 thing only locks the PCI bus! That is increasing the HTT to 201 or higher in bios. If you do this the ntune message will disappear, and the PCI bus will be locked, then you can raise HTT in windows. If you don't do this and you try and overclock in windows you will crash once you get past 220mhz HTT.
If you want to raise HTT in windows, download and use Clockgen NF4. nTune and AI booster are both trash, don't use them for anything other than monitoring unless you enjoy crashing your system. Make all other changes directly in bios multis, voltages, ram settings etc...
Overclocking is really easy and fun on this board, once you learn the tricks
And you will definately want to use a memory divider, you can get a much better overclock using memory dividers. Most people want to try and run ram 1:1 to get a high ram speed, but on A64's it just doesn't make sense. Always maximize you CPU speed, never sacrifice CPU speed for higher ram speed. 20mhz of CPU speed provides more performance than 60mhz of ram speed!