Preso direttamente dal sito di ATI:
DirectX Applications are limited to 60 Hz in Windows 2000 and Windows XP
Under Windows 2000 and Windows XP, DirectX applications may have difficulty switching to a refresh rate higher than 60Hz when run FULLSCREEN. The most common programs to exhibit this symptom are Direct3D games.
This issue can affect all display adapters and is not specific to ATI. Both Windows XP and Windows 2000 have a limitation in performing a complete enumeration of all the different modes and refresh rates for full screen. This issue and workaround for it is documented by Microsoft.
As of CATALYST™ 02.4, there is an added feature to override the refresh limitation imposed by both Windows 2000 and Windows XP when applications are run at a different resolution than the resolution of your desktop.
This feature should only be enabled if you are experiencing this issue.
To override the refresh rate limitation, follow these steps:
Bring up the ATI Control Panel and select the Displays tab
Click on the Monitor tab and you will see a new DirectX Override Refresh Rate
ATI Customer Care recommends selecting "Same as Desktop Setting" under the DirectX Override Refresh Rate option.