Warning: This FAQ discusses editing the system registry of your Windows system. Improper use of the registry editing tools (REGEDIT.EXE) may render the system unstable. I suggest backing up your current system registry. Refer to the online help of the registry editing tool for more information and be familar with both the backup and restore functions of the REGEDIT.EXE tool before proceeding.
Nvidia drivers may check for VIA 133 chipsets and disable 4x AGP if found. On most Nvidia based cards a simple DWORD value can be added into the system registry to enable 4x manually. The key to look for is at the following location in the registry:
Windows 98/SE/ME [HKEY_LOCAL_MACHINE\Software\NVIDIA Corporation\Global\System]
Windows 2000 [HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\nv4\Device0]
Add the following DWORD value to the above key: Name: EnableVia4X DWORD data: 1 (select hexidecimal)
Once set reboot the system. The driver should now run at 4x AGP