venting my new set up

Is it just me or is this ventilation business a pain in the ass? Ok...I will be getting a 400w mh / hps light for my 2' x 5' x 8' closet. I have easy acess to the attic through the ceiling in my closet. How do I vent / cool light and room. I see there are flanges or knock-outs on either side of the hood. I could get 6" or 8", and obviously the same diameter inline fan. How does it get attached? To hood? Does it pull air out of hood, or blow air onto light? I have been advised to have both intake (blowing) and venting (pulling)....can I get someone to explain to me how to vent this bad boy and keep room and light cool??

hey ive had a little experience with cooling 400w mh's and they get hot! lol
i would definitely advise getting an intake AND exhaust and atlest 8's if they fit, as for attatching them. im not sure.
all i know is they get hot, and can cause bad things, and as much ventilation as possible, especially in a closet, the better
hope i helped a lil