To avoid conflicts, you need to remove the driver you already have installed and then install the new driver in VGA mode.
Download
Microsoft .NET Framework 2.0, install and reboot. This is required for the Radeon Catalyst Control Center.
Download the
latest driver for the Radeon 9000/XP and save it to the desktop.
Go to Start > Control Panel > System > Hardware tab > Device Manager button. Click the [+] next to Display Adapter, right-click the ATI Radeon entry and select Uninstall.
Reboot and keep tapping F8 while the computer is starting until you see the Advanced Options menu. Select VGA mode. When Windows has finished loading, the display will look strange. This is only temporary while using the standard VGA driver. Disable your antivirus and install the new driver. Reboot to complete.