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.