How to identify what slot type a particular PC card is?

See if you can find your graphics card slot/connector in this hardware identification chart:

http://sonic840.deviantart.com/art/Computer-hardware-poster-1-7-111402099

Specifically, check the rightmost column, in the sections titled "Peripheral Cards" and "Desktop Card Slots."

Your spare video card probably uses a PCI-Express x16, AGP, or PCI slot. (listed in order from fastest/newest to slowest/oldest)

There are a few (very few) motherboards with integrated video that also support special pass-through riser cards. If that's the case, your best to identify the slot bet is to find a model number on the card or motherboard, and search on Google or eBay. But if you just need a card, you can get a card that will fit in any of your other expansion slots.

PCIe card (x16):

PCIe slot (x16):

AGP card:

AGP slot:

PCI card:

PCI slot:

And just for the craic, here's an ISA graphics card :)