I know this is probably a dumb question to ask but I don't really know much about graphic cards, so I was wondering how do I know if I have an AGP or a PCI slot on my computer?

What type of a system do you have (CPU and M/B)?

If you look at your motherboard, the "white" coloured slots are usually PCI; if it has a "brown" coloured slot then you most likely have AGP.

Here's an example;
http://www.lookout.ie/education/pics/motherboard.jpg