Well, the way I understand it is:
PCI slots are the ones that most computer have that allow you to slot in all sorts of extra gizmos e.g. a card that enables you to watch TV on your computer. They are (I think) usually located on the back of your tower and are relatively easy to access.
An AGP slot is one that is designed solely to take a graphics card and can't be used for any other purpose. Because of the way it is set up an AGP graphics card in an AGP slot will run far faster than the same graphics card in PCI version in a PCI slot.
Crystal?
Where the AGP slot is and how you know if you've got one I hand over to someone with genuine IT knowledge..........