The A7M266 has an AMD northbridge and Via southbridge.
You normally would install the AMD AGP driver, however, the one built-in to Windows XP is the same version as the latest one from AMD so you don't need to do anything.
You normally would then install Via's 4-in-1 drivers with the exception of the AGP driver. What Asus has on their website is labeled Via 3-in-1 drivers. (Via's 4-in-1 drivers minus the AGP portion.) Again, Windows XP has the Via drivers built-in and doing a Windows update will get you later versions than what's on Asus's website.
If you like to walk on the wild side, you can download Via's latest 4-in-1 drivers from their website and install those minus the AGP driver, but the ones available via Windows update work fine.