building a machine room

OK, I know some of you have done this -- Henk with his brick PDP machine room in the Netherlands, at least! Looking more closely into the power and other environmental requirements for my Onyx2 and other rack SGI systems, it seems prudent that I shouldn't attempt having these systems up and running without the appropriate environment. Fortunately the electrical isn't too bad -- 220 VAC, single phase. Its more the cooling and ducting part that has me wondering. At the moment, I'm not concerned with creating a building. I'm wondering more about what would it take to build a "machine room" inside an existing structure. Naturally, we're talking about building this on a "collector" budget and not what you would do if money were no object.

Assume you have something like a warehouse with a concrete floor but no warehouse-wide cooling situation. Is it feasible to build a small climate controlled room inside this larger structure? Where do you get the necessary A/C equipment for such a thing?