Upgrading my graphics card?

[Your Computer]

The Dell website (assuming http://www.dell.com/us/p/xps-8500/pd) doesn't say what motherboard you have, but it shows a Radeon HD 7870 is possible, so at least you know the case will have room for the GTX 660 card. As for the fans, i think the case already has all the fans it can carry (assuming one in the front and one in the back). You can probably make do with the current airflow it provides, but if you're planning on adding more fans, you're going to need a new case.