Well its an intel 945G chipset, not really the premier overclocker of those days. The 965 was the good board..
Im not at all familliar with it. If you could post the different choices you have in bios.
Maybe write down what you have to choose from in the core bios menu, then whats in there. Gigabyte had the "Intelegent Tweaker" section back then, so if you see that you can OC. If not, may not be many options to OC...
Only found one review:
Overclocking and Test System Specs
Well, this is going to be rather disappointing overclocking analysis. There are no overclocking options available in the Gigabyte GA-945GM-S2's BIOS. Considering the intended market for this 945G Express based platform this is not a big loss. There are basic memory tweaks though.
Doesnt look to promising... http://www.pcstats.com/articleview.cfm?articleID=2011
The 965 chipset was great for overclockng older 775 cpu's.. Unfortunately back then overclocking options were rare. Nowadays you see them on every board...