I'm having the same problem! I have an all-in-wonder 9800 PRO (128MB). It worked fine in Vista. The native resolution of my LCD is 1280x1024 (19inch) and yet I can't get it to go past 1024x768. I noticed that if I go into the catalyst control center > digital panel properties > attributes it says "maximum reported resoltion: 1280x1024". This makes me think that there is a driver issue or vista is limiting my resolution because my graphics card sucks? I can't believe that though. This card should easily be able to run a monitor at 1280x1024.

Anyone that finds a solution please post it here. I wrote ati as well. I will post if I find anything.