Most PCs post Pentium 4 have 2 PCI slots, 2 AGP slots, and a PCI-E slot. My old Pentium 2 had 2 ISA slots, 4 PCI slots, and 1 AGP slot.
Google the card types and you should find images of what the slots look like (ISA is usually black and long, PCI is white and medium length, AGP is small and brown. I've never really seen a PCI-E slot)