I would think the card would fit in any standard mid or larger tower case. It is not excessively big like the GTX its about the same length as those of hte last generation.
As for cutting anything to fit? Ask to speak to a supervisor at Gateway support and report those people if you still have the case number so they can see who worked your case. Its your civil duty to save the lives of many a GPU from these morons. You CAN cut the case if need be. A good dremel or rotarty tool and cutting disk will do. First off it probably will fit no problem. If thats not the case it may be as simple as notching the Hard drive bay area for hte card to fit. See exactly where the card will hit if it won't quite fit, then measure it up compared to the card.Then remove hardware of course from the case as metal dust/splinters wont' do your components any good at all. After everything is out, notch the HDD cage if necessary. Blow our/clean out case very thoroughly. Oh please wear safety goggles and gloves, metal and eyes/skin don't mix well either. If all goes well you can reinstall everythign and slide the card in.
Easy to do and you'll be the envy of anyone who doesn't know computers that well just because you now "modded" your own case to fit in a bad-ass card. Hehe. Good luck with it.