First off, I hope you didn't jump from stock to 260MHz? :-/
You have to go SLOWLY! Like 5MHz at a time. Check stability, make sure it's good, then go another 5MHz. After about a 15MHz increase, do a Prime95 torture test. If it fails, up the voltage a tad. If it fails again, you'll need a memory divider most likely. Then keep doing this until you reach desired speed.
You have an ABit board. I have an ABit board. Chances are great that the BIOS is set up the same way. So, go to "Advanced Chipset Features" and then find "DRAM Configurations". Now, find "DRAM Clock". You should see "Auto". Change it to "DDR333".
You have just setup a divider.
Your RAM will now run at 166MHz, so now it has about 33MHz of room before it is back at it's gauranteed speed (200MHz). That gives you a .33GHz overclock.
Goodluck, hope this helped.
Intel Q9400 | Gigabyte EP45-UD3P | G.Skill 2x2GB DDR2 1000 | XFX HD5870
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