Does anyone know what this does?

In dxdiag (directx diagnostic tool), there is a setting called AGP texture acceleration under the display section. This causes problems with some games (like Black & White 1) when enabled but work fine without. Does anyone know how this affects performance when disabled? Or even better, does anyone have the time to run a 3dmark or equivalent benchmark to gauge the difference?

Thanks in advance.

Can anybody test this for me? My main computer is having some problems so it'll be a while before I'm done formatting and setting stuff up