Xbitlabs has taken a closer look at the market’s different Radeon 9800XT and 9600XT-cards. They have chjecked whether the cards have support for Overdrive. The conclusion is that all 9800XT except the ASUS-card has support for Overdrive (ASUS has Smartdoctor instead).
Contrary to that some 9600XT lacks this function.
– How do you know if your Radeon 9600XT supports Overdrive?
You can switch on Overdrive and simply check. If you for some reason don’t want to test you can check on the card.
If you want to know more look here.