http://en.wikipedia.org/wiki/Graphic_cards

not really a hw forum BUT not all computers have graphics card slots, some only pci - this is because they have a igp (integrated graphics processor). If you only have 2 slot and they are the same I'm guessing they are both pci and will need a pci graphics card (they're not as good because of the limited data path) but they will work.

You should go to the computer manufacturer's web site and see the spec's and owners manual to see how to install a new graphics card and what kind it takes, if there's no agp or pcie-16 slot then you'll need a pci card.

According to the Steath web sit the s120 is a card for an agp slot (this is older technology) and a new computer would have a pci-16 (or such) slot for a grahics card. You could contact the manufacturer or place of purchse for assistance