"Even though there is no significant difference between 2x and 4x I always wanted to get 4x to work. I paid for 4X so damn it I want it! Now I found a way. It's called the AGP Driving Value. This value is located in the mobo's BIOS for those that use the VIA chipset. With some mobos the BIOS Setup program will have this option. There might also be an option called AGP Driving Control. This can be set to AUTO or MANUAL. Use MANUAL in order to set a value for the AGP Driving Value."
FULL STORY @ VIAHARDWARE (http://www.viahardware.com/agp4xfix.shtm)