An AGP card will not work in a PCI slot. You need an AGP slot on your motherboard.
These are Brown - PCI slots are (usually) white.
This is an explanation of AGP
Accelerated Graphics Port
A dedicated graphics bus slot on PC motherboards. Designed by Intel, AGP operates at 66 MHz and transfers data at a rate up to 528 MB/sec. By comparison, the PCI slot that most graphics cards currently use runs at 33 MHz and has a maximum transfer rate of 132 MB/sec.
AGP's greater bandwidth will allow game and 3D application developers to store and retrieve larger, more realistic textures in system memory rather than video memory, without incurring a dramatic performance hit.
Copied from Cnet Glossary.
Someone else may be able to give you more hep with your current set-up.