Nobody has even asked the important questions yet
How big is the room?
How many computers are in the room?
Is it on a first or second floor?
How well is the attic insulated? Are the walls properly insulated?
Do you have a window to do this with?
What temperature does it get outside / what area do you live in?
To more appropriately answer your question, I have a 14,000 btu unit in my computer room, which holds 2 computers. The walls and attic are all insulated, but it's on the second floor above the garage, which I think dumps extra heat into the room.
My 14,000 btu unit barely cools the room on hot summers.
well the room im in now is pretty small. think 1 car garage only cut off about 6 feet in back. it was originally a garage to begin with but the previous owners of the house converted it to a bedroom/office with better electrical wiring than the rest of the house before they moved out.
i had 3 computers running at the time, as well as 2 crt monitors in power save, and my 12x12x14 logitech sub woofer was on because my sister was listening to music earlier on it. left the computers running because they were all working on rendering various video projects that one of my friends is working on.
as far as insulation goes in here, the insulation is less than 5 years old, the attic above it is well insulated, and the ceiling is probably insulated better than it needs to be based on the difference in temperature near it vs around 3 feet off the ground.
room isnt on a second floor, but it gets hot enough you would think it was.
yes, i have a window that has a good bit of counter space by it to put this thing on.
if i forgot to state it before, i live in the sf bay area, and a lot of the housing around here doesnt come with central air conditioning for some reason that is beyond me.
now, as far as picking a unit goes, turns out that my buddy who i was lending my cpu time to just had the same thing happen to him (we have the same rig go figure), and he is planning on getting one of these for his room. says his sister got one when she went to college in AZ and it kept her 2 room dorm more than cool enough to live in on those hot days in summer. has good reviews and it apparently does the job rather well, plus it only costs $200
LG Electronics 10,000 BTU Window Air Conditioner with Remote - LWHD1006R at The Home Depot
ed: no im not currently running a lan center. however, when i move out of this house later this year, im hoping to move this hardware into a bigger room with enough space for friends to set their rigs up in. if i do that i will probably just get a second one of the units i listed above, if the first one isnt powerful enough to keep the place cool with 6-8 computers + monitors running at once. no, i havent talked to jugglenuts