Im still a little confused on what memory you should buy for certain FSB's. Should the actual clock speed of the RAM (not effective) be the same as the actual FSB e.g. not the quad/dual pumped speed?
Yes you want the ram to equal the FSB before it is quad or dual pumped.
So for example with a t-bred you will want pc2100 (DDR266)
For a barton with 333fsb you will want pc2700(DDR333)
Also keep in mind that if you want to overclock, especially on an AMD you will want the RAM to stay at a 1:1 ratio where as Intels can run fine (usually better) with a divider.
So if you have a 2500+ barton that you want to overclock to 3200+ speed remember to buy pc3200(DDR400) so it can run in-sync with the FSB which will then be at 200mhz.
If your motherboard supports FSB:Memory dividers then you dont need anything faster than PC3200 for an Intel platform. AMD rigs usually run best in 1:1 but for Intel it doesn't matter on the 865 and 875 chipset. 5:4 and 3:2 will run just as well as 1:1. Main reason for that being is because of dual channel. Dual Channel effectively doubles the bandwidth already so the need to run the RAM at high speeds for more bandwidth is no longer there. You just want to buy RAM that matches the DEFAULT FSB speed. After that you can just switch to a divider if you want to overclock.