We use our smallest room as an office. My husband and I each have a computer and so do each of our boys. This little space quickly becomes the hottest room in our house and is almost unbearable to be in. To top it all off, our clothes dryer is right outside the door, so the heat from that probably adds to the problem. I think you get the picture, but this is a very hot room. While there isn't a whole lot that can be done, there are a few good tips on keeping computers from putting out too much heat. Overclock.net answers this common question How can I cool my room down from my computer heat? This short article talks about lowering the amount of heat certain parts generate by lowering their voltage or frequency, which although technically possible is probably pretty extreme for most people.
In a room like ours, it helps to make sure that any computer that isn't in use is powered down, by setting the power management settings appropriately. It helps, a bit..
I would rather work on a laptop under a shaded tree in some quiet park, but for now, this is my workspace and it sure needs cooling down. If your office heat is getting to you, try some of these tips, but don't forget the obvious; leave the door open, and add window and desk fans, they go a long way too.