AGP is a short for accelerated graphics port. Old computers (well - this depends on how long you have been involved with computers ;-)) have usually one AGP slot which is intended for the use of a graphic adapter. For more information you might want to consult Wikipedia
A video graphics card goes in a AGP slot. ( AGP: Accelerated Graphics Port )
Graphics card.
graphic card
mastercard or visa
Only graphics cards are inserted into a PCIe x16 expansion slot.
PCI
pci express or AGP
AGP Video card AGP retention mechanism = AGP Video expansion card
A network interface card can be connected to a standard PCI slot or PCI-E slot. The choice of what slot to use is up to the person building the system and also based on what expansion slot is unused.
No a type II card is twice as thick as a type I slot (but a type I card WILL fit in a type II slot)
Take a look at your system motherboard to see if it has an AGP or PCI Express card slot (it will be the topmost expansion slot on the motherboard--your monitor should be connected to the card currently sitting there). This will tell you which type of video card is available to you.
PCI, PCIe.
Desktop : standard PCI slot, usb dongle, and NOW there are PCI-E 1x cards Laptop : PCMCIA slot, usb dongle, or built in :D
A video card is plugged into an expansion slot on the peripheral bus. The exact type of peripheral bus slot varies according to the type of motherboard used. Originally, video cards were plugged into an ISA slot. Eventually they went in PCI slots, then AGP slots, and today, PCI-Express slots. Regardless of the type of peripheral bus interface, the peripheral bus connects peripheral cards, also called expansion boards, with the system chipset.