If you installed x64 Windows 7, you have no chance of finding a driver for that. If you installed x86, I could possibly hack one to install for you. Which did you install?
Look in the device manager and tell me which exact ATI device it is.
Also, right click on it. Properties. Details tab. Change dropdown to hardware ids. Copy and paste results to here.
If there's anything possible at all, I'll do it for ya.
Edit: I think you have the 320M which only has 64MB of RAM. Because of that, Aero will never work or be enabled.