Hi
Ati makes their drivers to work with all their vid cards, save for the very oldest. Most card makers do so anymore, and call it a "unified driver architecture." I call it one size fits none, for a few good reasons. You should be able to run any cat driver they make/have made. Ati drivers are called "catalyst," cat for short.
Now as to what driver to run you have some fine tuning options: the 4.xx, especialy the 4.10 cat is optimised for d3d games and UT games in particular, use them if you play mostly d3d games.
If you play mostly opengl games, use the latest series, the 5.xx types. These are optimised for opengl and cards that have less than 256mb of mem on the card. The 5.xx series are simply awesome for opengl.
You can't go wrong with the latest drivers for any video/game api, either d3d or opengl, but there is a performance difference between them depending on the api the games you play use. If you want max frame rates use the driver suited to your game.
