Theres a difference between PCI and PCIe
In essence, if your motherboard doesnt support PCIe dont waste your money on upgrading the graphics card - put the money towards a new tower.
AGP is accelerated graphics port. Its just the bus ( slot ) type. Its old technology as previously stated.
It will usually say PCIe in small white letters to the side of the slot if you have it.
If you take the side off your pc and give us the motherboard make and model then we will be able to assist further
