What about DOS ?

From memory, you won't get the option to install the AGP drivers at all under XP since they're already installed. I'm probably be wrong about that, been a while since I've done it ! I mentioned this in another thread somewhere too but I've read that you can run the 4 in 1 setup under 2000 compatibility mode and it will install the AGP drivers, therefore giving you the option to select "turbo mode". I haven't tried this myself so I don't know if it works.