Your motherboard uses an nVidia chipset. They overclock a little differenly.
This should be your first stop.
Core2 Overclocking Guidehttp://www.tomshardware.co.uk/forum/259899-11-core-overclocking-guide
Next stop should be a guide for your particular motherboard. Google is your friend.
Go through the guides. Then take your core voltage off Auto and set your memory voltage to factory recommended values. Change the memory frequency from AUTO to either Linked or Unlinked - whichever you need to set the Memory Frequency to half the FSB clock or twice the FSB frequency (same thing). At the stock FSB frequency of 333 MHz, your memory frequency should be at 667MHz and the FSB clock should be at 1333 MHz.