I haven't done this in a couple of years and am kind of hazy on it. I recently bought a Mach Speed V2DP motherboard, AMD Sempron 2400+ Socket A Thoroughbred processor, and 512 MB of Kingston PC2700 DDR Ram (333 Mhz, or 266). The board is rated for 200/266/333 FSB. As you may have guessed, I'm not building a state-of-the-art system, but trying to economically get a few more years of life out of my old 450 MHz, P2 system. For front side bus frequency setting I am given a choice of 100 MHz, 133 MHz (default), or 166 MHz. I've been researching, but haven't been able to find crystal clear (which I need) instructions as to how to arrive at the correct setting. I would appreciate any input on this subject, and feel free to include the math behind the choice.