This could be a bit tricky. Cards are "dual slot" in the sense of being the width of more than one slot. But they don't actually USE two slots. So if you only have one PCIe slot on your mobo, but there is empty space next to it and your case will fit the thing, you can still use a "dual-slot" card. Check inside your case and on the mobo to see whether you have more space, and check the side of the case two for where the ports from the video card would line up.
Thank you sooooo much for clearing this up! You don't know how much this helps!