In display properties, change your display adaptor to a Standard VGA Adaptor and delete the Banshee's drivers. Shut off your system and pull the Banshee and replace it with the Radeon. '
If your switching from a PCI card (Banshee) to an AGP card (Radeon) make sure not to put some other card in the first PCI slot next to the AGP slot.
Boot up your system and after Windows detects the Radeon, install the drivers. Once you have settings the way you want them go online and get updated drivers.