Need ventilation ideas???

My grow room is 10'x10' split in half, one side for seedlings,clones, & vegging, and the other side for flowering. On the seedling/veg. side I am using a 4ft 2 bulb floro. for seedlings, and a 400 MH for vegging. On the flowering side I am going to be running 2 600 HPS. I Have a portable A/C & fans in the room for heat control and air circulation. My problem is that I don't wanna cut any holes in the ceiling or walls to run an exhaust. I have my A/C exhaust running out of the Central A/C vent in the floor.(the duct underneath is unhoooked and capped off) Do you have to have an active intake and exhaust system or will i be fine. Any help would be greatly appreciated.

IF you have just a intake and not an exhaust the air will choose it's own path of exit. leading to the possibility of smell going with it. (not usually a good thing to have occurring). Is there a dryer vent near by?

Thanx for the reply, there is no dryer vent nearby. I am not really concerned about the smell at this point because the place always smells like weed anyway!!

You really need a proper ventilation system or your plants will not grow properly and perhaps die. Could you not try and run an intake and an exit through your AC vent? Its far from ideal but it would help. If you were to do this you would need to try and get the ends of your exhaust and intake pipes away from each other so that the same air does'nt keep circling around.
Good luck mate, hope you get it sorted, would hate to see some1s crop die.