I have a friend who has a "babygated" community (her computer room) for some of the older cats. She has 2 dogs, one of which will not leave the cats food and water alone. So, she put up a baby gate with a hole in it just large enough for the cats to get through it, but keeps out Sydney (the puppy). Works great. The cats eat in peace.

As far as keeping both litterbox AND food in the same room, not a good idea. The food and water shouldn't be near the litterboxes, at least that's what I've read in books and stuff.

I keep my cat's food in the kitchen and the litterboxes in the bathroom.