I've been finding more and more, that the newest drivers are not always the best performers with older hardware. After and extensive search for earlier versions of ATI's Catalyst drivers, I found this site.

http://oldapps.com/list_drivers.php

Both ATI and NVidia drivers are there, back to some of the earliest versions. Very useful.

I've only tested the ATI drivers, but they are official releases, not hacked or tweaked.