There are generic AGP drivers for the Intel chipset, but if you have not loaded the INF files for the motherboard, you are probably being restricted to a lower level of performance.
Still,..you are CPU limited. Tha 1.7 P4 is the old Willamette core, which was pretty slow.
When you removed the NVidia video drivers, did you use a third party driver cleaner to make sure the drivers are removed? That can also effect performance.
You should be able to set the in-game resolution to 1600x1200 and have the same frame rate,..only it will look better.