If yours is the same as mine it has a default clock of 155mhz for core and memory, these early radeons like same clock speeds of memory and core otherwise they lockup or unstable in games. So..The memory is rated for 166mhz...the card definitly overclocks to 166mhz easy..above that you may or may not get graphic glitches in windows and games just depends on how your luck goes. Thats just teh way the card is, I have added a fan to the stock heatsink, My card does 170mhz fine...I have no heatsinks on ram as they do not need it, never get warm.
Pinky has overclocking tools on his site listing in his sig, I use Radeon Tweaker...
I love this card it hauls azz in Tribes 2...my proc is whats slowing me down a bit...