DDR
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Double Data Rate SDRAM. PC2100 is rated for FSB of 133, PC2400 is rated for FSB of 150, PC2700 is rated for FSB of 166. Multiply by 2 to get the effective performance of DDR. 133=266, 150=300, 166=333.
The 4:3 thing is probably the PCI divider. The PCI bus runs at 1/4 the FSB, when the FSB is at 133+. So at 133, everything on the PCI bus is running at 33Mhz. At 100 FSb, it'd use the 1/3 divider. So at 100, it'd still be running at 33Mhz. By overclocking the FSB, the PCI bus and everything on it runs faster than its specifications. So, at 150 FSB on a 1/4 divider, everything on the PCI bus would be at 37.5 Mhz. Very often, PCI cards or HDD's will have problems running too far out of spec.
FSB adjustment should be somewhere in your bios if your motherboard supports such adjustments. It might be labeled "system bus" or "front side bus".
Ask about it in the Motherboards section and you should get answers from people who have or have used the same motherboard.