New Grower: Need some help

Hey guys so I have a 400w unsealed hps light that im looking to use in an 8 by 4 closet. My first question is can i use 400w hps and metal halide bulbs in the same ballast interchangeably, and secondly how can I properly (and cheaply) ventilate this unsealed demon so that my room doesn't get to be like 100 degrees. Thanks any suggestions would be greatly appreciated.

no you cant use MH & HPS in the same ballast, UNLESS it is "switchable"! you can get "conversion" bulbs that allow you to run MH in a HPS ballasts.
I keep saying it, so other members are probably getting tired of seeing it....BUT check out "NORTHERN FARMERS HP STADIUM GROW". Not less that a month ago i spent $2500 on my room, now i want to change it into 2 "mini stadiums". NF has fan blowing in from 1 side with his exhaust pulling out on the other side with the lights in the middle being cooled by the current the intake & exhaust make. pretty cool , huh?