Overclocking a graphics card is easy - just go to:
http://www.entechtaiwan.com/
And download the latest version of PowerStrip. Once installed, right click the icon in the system tray, then go Performance>Settings. You should see 2 sliders, one for RAM and the other for the GPU. Start by adjusting them in 5Mhz increments, and test for stability in between. Don't go all at once, as theirs no way to tell how far you can push your card as it's different from everyone elses.
Once you start seeing artifacts like stray pixles, noise etc... it's time to back off. Then, loop 3DMark2001se for a good several hours to check for stability.
Hope this helps,
Foxy