Hey, I had the same problem. This is how you enable AGP;
1. Get RivaTuner, and make sure it is Release Canadate 11. Find it in the download section of any 3D website base.
2. Ensure you have the lasted Nvidia 29.xx drivers (I have the latest Nvidia-blessed ones).
3 Update your AGP driver should haven't already done so. If you have an ALi, then get the 1.90 AGP driver.
4. Extract RivaTuner into its own folder, then run it.
5. Go to the PowerUser tab, disregard the warning, then look at the bottom for the folder icons. You want the second one from the left which when selected displays "Open matched Detonator database." Click it.
6. Once it loads, find the fifth line, it should say, "NVIDIA Detonator 29.4x w2k(even if you have XP) System."
7. Once found, scroll down to "Enable Ali AGP." Right click it, click the lighted bulb, and make sure that "1" appeared in the right-hand "Value" column. Exit RivaTuner and reboot.
8.Once rebooted, initate a directx diagnostic and you should find that you can enable the AGP texture acceleration.
Later and take care, Raj