AGP is vastly superior to PCI. The most recent hardware is PCI_E.
AGP 8X is 8 times faster than PCI. PCI_E is 16X. Your board might only run AGP 4X however.
We need to ID the motherboard to check the specifications and limitations.
What is listed under CPU_Z for Mainboard > Manufacturer and Model?
http://www.cpuid.com/cpuz.php