Video Card Question

[Johnny Holdem]

I would open up your computer and check for power supply, usually written on the power supply somwhere the voltage.

As for AGP and PCI, your mobo probably came with 5-6 PCI slots, and 1 AGP slot, if any. if you computer is standing upright, it's the top most slot right above the 5-6 PCI slots.
Mobo picture

As for the slot in the back with the monitor pic, not sure, might be an extra video port.

What kind of computer do you have? Dell? give us a model number and name.