Could anyone tell me how should I know when to stop increasing a video card's core and memory clocks?

I have a Sapphire Radeon 9600XT / 256 mb
Its original core clock speed is 500 MHz
Its original memory speed is 250 MHz (I thought it was 300 but when I installed PowerStrip to overclock the card it said it is 250)

Is there anything better to overclock a video card?

TIA

Mat

Do any of you guys know where I could find a stability test program/utility?

Something like ATITool could be what you're looking for.

The general rule of thumb with overclocking video cards (at your own risk!) is to keep on increasing the core and memory in 5-10Mhz increments, testing with a 3d app each step of the way (although you might want to do a bigger jump in clockspeed at first). If 3d app displays lots of graphical artefacts (corruption - you'll know it when you see it!), then clock back until it stops.

Yesterday, I overclocked it at 550 for the core and 280 for the memory. I ran 3dMark05 and then, the valve stress test to see what it looked like. In the stress test with the original settings there was purple on everything with transparency like water and glass. With my new settings, the purple was gone!!! I found it a bit strange but hey, it's fine with me! I then tried to higher the memory clock by about 7 but the screen started displaying vertical dashed lines and distorted text. I figured I had to bring it down a bit.

Thanks for the tool. I'll take a look at it tonight after work.