@marczellm Go to AMD.com, click Drivers & Support, and in the Manually Select Your Driver select Desktop Graphics, Radeon X Series, Radeon X8xx Series, then choose either 32 or 64-bit Windows Vista for the OS and download the driver.
After downloading, run the installer, and let it extract the driver to C:\ATI\whatever. Afterwards, the actual driver installer will run, but it usually fails - don't worry, close it, go to Device Manager, right-click Microsoft Basic Display Adapter, choose Update driver and tell it to search in C:\ATI. You'll most likely get a question if you trust ATI to install the driver - do so, and the driver will install and work fine.