You're probably going to want a better power supply to run a GTX660. The GTX660 is a fine graphics card, if a little bit out of date now, but if your power supply can handle it (which I suspect it can't), it'll do fine for most things.
The GTX750 is a card that probably wouldn't require a power supply change (it doesn't require any additional power connectors, and it uses extremely little power for a GPU of its capacity, though check that your PSU can handle the extra load before putting it in and trying it), and you can probably get it for about the same price as the GTX660, so it might be a better fit for what you're trying to do.
If you list your PSU's model, we can probably tell you whether or not you should think about upgrading that as well.