I don't know the actual frequencies, I may try and find out if no-one else can help you, although I think the aircon in our server/equipment rooms is louder than the equipment itself.

Best thing to really sound proof the room is to decouple it, or (to put it another way) float a room inside the room and stick everything inside the floating room. Now this will be impossible (I suspect in your case), and I can't remember what the best method of doing it is. The next best thing is very heavy and dense doors, something soft to dampen the sound (like hessian on a frame held away from the) thick walls (preferably with a void in between) with a seal around the door, to prevent sound leakage. You can get retractable bottom of door seals (we have some here at work, but in other areas) that do so when you open the door, not sure how effective they are.