I've got 4 42 watt 6500K CFLs in a very small space and the temp shot up from 72 (with 2 bulbs) to 82 (with 4 bulbs) in a night. Opening the window (on cool days) in the room of the closet and/or adding a small oscillating fan remedied the problem. Placing the fan in such a way that the fan blows up at the lights dropped the temperature back to 72 degrees (the temp with only 2 42 watt 6500K cfls). I'm a total noob, but this is my experience with 2 - 4 cfls in a small space.

As the plants progress and more bulbs are required, it may be neccessary to provide a more elaborate ventilation solution. However, in my studies of others' CFL grows complex ventilation was never required.