To fit it in a slim atx case you would need to get an itx motherboard or micro atx motherboard(whichever fits the specific case), but you would also have to get a low profile video card. The 750 and 750ti are supposed to come out in that size soon, but I haven't seen any at major retailers yet and they'll most likely come with a $20-$40 premium. That size case would seriously limit your upgrades later on also, because normally there aren't even cards above $80 or so in that size.
One option might be to just get the smallest full size case you can find. I've used this one before without any problems and it fits a full size ATX motherboard, video card, and full size ATX power supply, but it's really small in size.
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119262
Another option might be something like this. It requires a mini-itx board, but it fits a full size video card and full size power supply.
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119261