Ceiling of my closet opens up on it's own... Good for heat you think?

I'm about to buy a 150 hps and a some CFLs to grow a few plants (3-4) in my my 7x4' closet. This closet has a 1x1' foot piece of wood on the ceiling that slide over and gives way to the attic. Do you think I could just open this up and maybe put a screen in it's place, you know, so like animals or whatever is up there don't drop in. Do you think this will control my heat by allowing it rise out on it's own? Or will a hot attic cause my closet to become hot? What do you think?

Yes it will help a lot, might even do the trick. You could always put a fan in it to suck the air through the closet. Just be sure there is room at bottom of closet door to let air in either way.
FWIW - If you got animals in your attic you need to get rid of them, they'll eat your wiring.

Sound likes a plan but that amount of light I would do more than 1 maybe 2 plants. Just my opinion.

Is probably big enough to separate into a veg and a flower room if there's access.... the more the merrier...

I had a setup almost exactly like that for my first grow with an opening in the ceiling to the attic. That opening is your ticket to great ventilation (plants love fresh air) and reducing heat (plants don't like excessive heat). You can do a lot better than a 150 and some CFLs. You can put a 400w in there so you can have more and more vigorous plants and a much better yield. Get a small inline fan and ducting so you can pull air in from one part of the attic (unless you have another source of fresh air), and another inline fan to exhaust to another side of the attic. Apart from that, a small circulating fan inside and you're set.

sounds cool dude i agree with sarita i would use atlest a 400hps in there maybe in a cooltube venting into the attic
why not keep the wood there i hope there isnt animals in your attic anyway! the attic wont add heat it will just take it away as all the heat will
just raise up and all go into the attic