i just ordered a 2mx2mx2m and got a 1000w hps with 6" cool tube. if you live in canada check out some ebay sellers this tent and light setup was cheap for me.
i got the tent
1000w digital ballast
1 hps bulb
1 mh bulb
6" air cooled shade
6" carbon filter
2x 4" 270 cfm inline fans
6 sets of rope style yoyo hangers
for about $650 after shipping.
i plan on having one fan for the light that will draw from outside the tent go through the light then back outside the tent (all sealed) being such a big tent the temps should not be so bad this way.