What monitor do you have?
Resolution limitation is the worst of your Graphics Card and Monitor.
Your Radeon 9700 Pro defintiely does not have that limitation, but 15" monitors and smaller would have probs going higher than 1024x768, Besides, those smaller monitors would make everything too small to view comfortably in higher resolutions.
This goes for smaller LCD screens, like on laptops and Flatscreens, as well.
The only mintors that you would even want to consider higher than 1024x768 would be 19" and above.
Now all of that aside, if you have at least a 17" montior, you should be able to view a higher resolution. You may need to remove your graphics drivers and reinstall them, as they may be corrupt. Howveer, unless there is soime need for you to do this, and you have no other problems, then I would recommend against it.
What Operating System do you have?