i have a 533 FSB 2.8GHz P4, an P4S800 MoBo, and PC3200 RAM. My Bios doesnt let me set the FSB but the boardspeed / PCI and RAM speed only. any body know of some equation which works out the full speed using the RAM freq. boardspeed/PCI speed, multiplier?

the 'ram speed' will make your fsb speed what it is, and leave your PCI bus alone, thats out of the ballpark.

for every 1mhz you bump up your ram speed, your fsb will increase by 4mhz.

so why under processor speed does it have boardspeed/PCI speeds? and not any regular FSBs? (e.g. 133, 533, 800) the selections range from 133/33 to 266/44

I think I know where you're getting to.
Have a read on this link below. Hope it will help you to underestand more about FSB.
http://www.pcvsconsole.com/hank/answer.php?file=499

no i dont think it is anything to do with quad pumping, i just need to know how to set my FSB using the selections available which is the Boardspeed/PCI speed, they must have something to do with the final speed of the processor cos thats all my bios allows me to set (aswell as my RAM freq).

First of all, sorry for misintepreting your question. After some research, i have found out the following:

In order to set the CPU FSB manually, you will need to set the board to "JumpFree mode".

Under Advanced menu, on the top row there is this "CPU Speed" row, set it to [Manual].

After that, I m pretty sure you can change the FSB manually.

Hope this really helps this time.

no thats the problem, when set to manual it ungreys the field called "CPU external Frequency (MHz)" and in the selections for the values of this field are board speed/PCI speeds. at least that is what i have been told by Asus when i contacted them to find out what was going on.

Changing the PCI speed will affect things like Sound. You want to leave that alone.