Graphics card help

I'm not sure if this is the correct place to post this but I saw a similiar thread that helped some and it seems that this is a very active community.
I recently purchased an Inspiron 580 (I apparently got the minitower version and not the slim version). I want to use it for gaming and need to upgrade my video card (currently only has an onboard video card).

Now I do have an Nvidia Geoforce GT240 1 GB DDR3 from my previous computer but this video card wont fit in the tower (it seems that the PCIe slot is about 1/2 inch to high and the external portion of the card does not match up with the punch out slot in the computer case). So how do I find a video card that will match up with my computer. I went to the dell website and they gave me a list of video cards to potentially use (Graphics Cards : Computer Components | Dell )

I am willing to upgrade my power supply as well.

If there is a PCI-E slot, it should fit, are you sure you are putting it in the right way? Just don't force it.

Weird.

I wonder if the 580 mini-tower requires a half-height (short) graphics card. On the link that you provide, three of the four are half-height (with brackets for standard slots as well). The exception (Radeon 5850) is definitely not half height. It also probably won't work with your stock power supply.