U mean you OC the proc and the ram also increase ? Thats normal la.. If you want a stable system, increase up your proc speed and try to maintain your ram speed/lower it a bit ..

Yeah i know, coz i have try it to make 1:1 but always 1:2 come out ..

Usually most GigaByte motherboards have more flexibility when it comes to overclocking. Example is the Pentium D 945 3.4GHz overclock to 4GHz as shown in my siggy's CPU-Z tag. 

Another example here: Pentium Dual Core E5200 (with GigaByte GA-G31M-ES2L)...



Here is a simple guide..

Your RAM speed configuration should be under "Chipset Configuration" page . Also check in your motherboard manual, there should be FSB override jumper settings.. find "OC 800 / FSB0 / FSB1 Jumper". 

The GigaByte GA-G31M-S2L has basically the same options as the GigaByte GA-G31M-ES2L as shown above, thus its mostly down to playing around with memory ratio and memory voltages (always try to keep the memory speed as close as possible to factory specifications, or at lower frequency than default). A newer board, the GigaByte GA-G41M-ES2L has even more stuff to tweak, including the memory timings (check this review).

What is current processor? What is the clock speed and FSB frequency?

TS's motherboard has BSEL override jumper.