yes i have an pci-e slot the graphics card it self isnt that hard to find its the power supply that is the bug obstacle at this point. are u familar with the external power supply for graphics cards such as the Asus XG Station.
We just had a few threads similar to this one involving Dell and HP slimline cases with slimline power supplies. A 300 watt slimline psu is about as good as it gets in the USA. Your Gateway model has a 220 watt power supply and is only 4.2 inches wide so you'd also have to install a low profile video card.