AGP Driving Value is an option typically associated with many boards based on a Via chipset. It was created to help ensure compatibility across the wide range opf AGP cards.
The AGP Driving Value determines the signal strength of the AGP bus. The higher the value, the stronger the signal of the AGP bus.
It is listed in a range of hex values (00 to FF) which translates into 0 to 255 in decimal values.
By default, the AGP Driving Value is set to DA (218) on all Via based motherboards.
AGP driving value is to help compatibility, it will NOT enhance performance at all. So do not change it if your system is already running stable.
Be carful adjusting the signal strength as this is one of the easiest ways to cause irrparable harm to your video card.
There is no specific setting that is better for all cards. Each individual chpset is different and may have very different tolerances to the AGP signel strength. If your not experiencing instability or incompatibility with your current video card then leave this option alone.
If you are experiencing issues then ask here or ask someone else who understand this as this is one of the surest methods to damage your card if you improperly choose the AGP signel strength.