The front side bus for a C2D runs at 266MHz. The motherboard, depending on you RAM will run the RAM at a faster frequency. If you have DDR2 533, it will run the RAM at 266 MHZ (DDR2 works twice per clock cycle) - so no difference between the RAM speed and the FSB. For 667MHz DDR2, it will run the RAM at 333 MHz, by multiplying the FSB by 1.25 (or 5:4 ratio).
Your motherboard will look at the SPD values on the RAM to decide at what speed to run it, and what the various other timings to set it to. This should all happen by default. Sometimes, some BIOS revisions for a motherboard aren't very good at detecting the RAM settings, but it usually works.
EDIT
As for overclocking, read Wusy's sticky in the overclocking forum. It says when starting to OC to change your RAM back to running at 533 MHz before increasing the FSB. This is because your CPU (unless you have the X6800) has a fixed maximum multiplier compared to the FSB. So for an E6600 like I have, the multiple is 9. If FSB=266, CPU=2400. Or if FSB=300, CPU=2700.