I am using 9600GT 512MB, the graphic card come together with a software (called Gamer HUD) that allow me to overclock my graphic card by pulling the bar show in the interface to higher frequency, the software allow me to adjust GPU frequency, shader frequency and memory frequency. But it warn that too much overclock may damage the graphic card. Is this true? How much overclock is consider too much?

Now all the frequency level are in default which is about half of the maximum performance.

So far i havent try and not dare to try overclock my card.