I am going to get 6 cfls.. and yes, i am also getting a box fan.your pushing it with the height, its only 2 1/2 foot high so by the time you take the pot size and light distance from plant you will be lucky to have 1 foot for the plant height, even the 150 hps will heat that space up alot, i think cfl is the way to go for this, however if you can control the heat off the hps then go for it, you will need more than a pc fan to keep it cool though, probs a 4 inch inline fan with some sort of small cooltube. or keep the door open when lights are on.
ok thank you so much. i have 24w cfls.depends on the cfm it pulls, 6 cfl (depending on wattage) wont heat the room up to much so you might get away with doing it the way you said above, 2 out 1 in, if its still to hot have all 3 out and passive intakes.