Marine-proofing a Computer

thaddjuice writes: "I'm interested in installing a computer on my sailboat to interface with the ship's navigation and communication systems. What I'm wondering is what needs to be done to a computer to protect it from salty air, potentially damp surroundings, and temperature extremes. What parts are most vulnerable? What about peripherals - can you protect keyboards, mice, and monitors from these conditions? Power is also a concern, it has to run off of boat batteries. Should I start with a laptop, desktop, or rackmount system?"