Welcome.
Unfortunately you have 2 strikes against you. The CPU isn't the best for overclocking, but you might squeeze a couple mhz out of her. Your motherboard won't handle overclocking features, you'd have to use a windows program to increase your bus speed (and in turn increase the processor speed).
In my signature is a link to software I keep handy. Download Softfsb from there and try increasing your bus speed a couple mhz at a time. I also recommend reading the tips section on our homepage for some guidance.