Overclocking graphics cards
 

I am waiting for my new pc to arrive in the post. One of the many parts is a gigabyte geforce 6800GT PCI-E. Can I overclock it without changing voltages etc. I saw on a web site that to overclock it you move a slideing bar if you know what I mean to increase the memory and core speed. I would like to make it run at the same speed at the geforce 6800ultra. Will that require me to buy another heatsink and fan because I have read that the standard HSF is really noisy.