Hardening PCs for Hostile Environments?

labradore asks: "I must install a 1.2GHz Athlon system, in a secure place, at a retail business. The PC is going to be a security video recorder and a point of sale terminal server. In other words I need it to act like an appliance: something that requires very little on-site maintenance and at most, remote adminstration. Unfortunately the only secure place to put it is inside a hot, dusty storage room. It has it's own protective lock-box (approx. 3x3x3 ft.) to keep evil employees and snooping types out and to insulate it from the heat and dust of the storage room but I don't know how to actually keep the box cool and fairly free of dust." What things would one need to house comodity components in such a way to enable them to survive in such hostile environments? Is 27 cubic feet too small for the necessary modifications that would have to be made?

"There must be a lot of other people turning PCs into "embedded" controllers or appliances facing the same situations. At the very least this could be thought of as the quest for the ultimate "fire-and-forget" cooling environment. What options has the collective mind of Slashdot uncovered and thunked up to deal with this kind of situation?"