First off you should google Overclocking and find as much about it as possible.
Right were ready to begin
The e8400 has a 9X multiplier and a base FSB clock of 333. So 9 X 333 = 3GHZ with 4 X 333 = 1333MHZ FSB.
You want to acheive a 1:1 ratio between your cpu and ram. In your case your ram is 800mhz so a setting of 400 for the fsb is what you want.
RAM = FSB x 2
So 400 x 2 will give you 800mhz
If the E8400's FSB base clock is increased to 400 you get an OC of 3.6GHZ (400 X 9) with a FSB of 1600MHZ (4 X 400).