Minecraft wiki entry for Furniture, associated text: Place an iron block, a painting on the side, and a "keyboard" in front of it. Some people use a powered minecart rail, mostly because it looks like there's buttons on it in the original resource pack. Best use with a desk. Some people put an item frame with an apple on the back to brand it as an Apple iMac! You can use 3×2×1 logs and put the "computer" in the middle. Alternatively, there are several mods that can provide you with computers. A good example is ComputerCraft or the Mr. Crayfish's furniture mod.