Part of the problem is the antiquated SiS chipset on your motherboard (741GX, 963L), and either very limited support for the AGP controller in Windows 7 or outright no support in the native AGP driver.
One thing to try before installing any ATI driver is to install this, SiS - Welcom to Silicon Integrated Systems Corporation.
using Compatibility Mode, Drivers - Install Vista Drivers on Windows 7
and then, again before installing the ATI driver run Windows Update and there should be an update for the AGP driver. Then the ATI driver should install, of which only the AGP Hotfix driver, Catalyst AGP Hotfix - Radeon HD 4000 Radeon HD 3000 and Radeon HD 2000 Series AGP products
will work with your card as there is no support for the HD 2xxx series and up AGP cards in the regular catalyst drivers.