Thanks to DosFreak for this one:
ZTAGPTool 0.13

This is a small program to change numerous settings on the AGP BUS of modern computers. It is currently able to set:

AGP (ability to turn off all AGP capabilities)
AGP-Rate (AGP 1x, AGP 2x, AGP 4x, AGP 8x)
AGP Sideband Addressing (ON/OFF)
AGP FastWrites (ON/OFF)

Download