Avoid moving parts... (Score 4, Informative)

Previous posts made the point of sealing up the computer and monitor... all fine and good. Be sure to get a keyboard that's sealed, and an optical mouse, or a touchpad. There are "roll-up" keyboards that have no exposed moving parts. Also, if you can enclose the computer & monitor in a housing that has a "positive pressure", you'll avoid a lot of the trouble dust. Try to find a way to blow clean air into the enclosure so that no dust can get sucked into the cabinet.