Core2 Overclocking Guide - generic guidehttp://www.tomshardware.co.uk/forum/259899-11-core-overclocking-guide
Shadow's Gigabyte motherboard OC guide:http://www.tomshardware.co.uk/forum/page-245679_11_0.html
It's for an EP35-DS3L but all the Gigabyte Core2 BIOS's are similar.
Go through the guides. Then take your core voltage off Auto and set your memory voltage to factory recommended values. Change the System Memory Multiplier from AUTO to 2.00, 2.00B, or 2.00D - whichever you need to set the Memory Frequency to twice the FSB. Then when you increase the FSB, the memory clock will rise in in proportion with it. At an FSB of 266 MHz, your memory clock should be at 533 MHz.
Download CPU-Z to check your FSB:RAM ratio. It should be a 1:1 ratio.
Now you can start pushing the FSB up.