With the mac you'll probably need an adapter to connect to the vga port on the projector. The pc will probably have a vga port on it.
You can probably get hd projectors, so they might have a different port and that may mean you need an adapter for either computer.
Does the gallery not provide the projector?
As for sound, you may find that you need either a 3.5mm (like a headphone) jack to 3.5mm or 3.5mm to 2 phono plugs, depending upon the projector.
Or you could use speakers.