you just need to go into the softmenu and then where your CPU speed is displayed change it to "user define". If it is still at stock speed it should say 100 1/3 and the multiplyer will be 7. you will also need to disable speed hold error, which is in the same page just a few rows down.
So when you get to user define you can then change your Front Side Bus, FSB, to what ever you want. My Abit BE6 has a 105,110,115,120 with a 1/3 devider and 124,133,145 and 150 with a 1/4 devider.
Here is the catch, if you go to a FSB of 133 you AGP slot will be running at a speed of 89mhz and not all video cards will do that speed as they are usually run at 66mhz stock.
right now I have my Flip chip 700 at a FSB of 124 with the PCI at 1/4 but my video card is at 80mhz.
What kind of video card do you have, what model board is it? You will also need a good cooler for your CPU.