For each 400watt light, you will want about 2'x'2 to 2'x3' feet of floor space. For the veg stuff, you can make that super stealth with some CFLs, computer fans, and a small cab. The flower howerver is a little different.
I used to grow in a utility cab, but they draw quite a bit of attention when they don't match anything in your room and every one is wondering why you have a giant cab in your bedroom. Plus they usually don't come in a size any wider than 19", and that extra 5" to get to 24" makes a big difference.
I used to grow in my closet as well. It was one with sliding doors. This worked ok as long as nobody slid the one door open. If you have a walk in, this would work better, but there is really no way to exhaust it without cutting holes in walls and doors.
A couple of dressers is ok, but you won't be able to fit all of those lights in there. You would have to have one for each of your lights, and they are hard to find in a 2' width.
False walls will work, if you don't mind your bedroom being tiny. You'd be amazed at how much 3' actually takes out of your room.
All of these ideas will work, but if you really want it stealth, and want to be able to have people over to your house, and in your room, etc, you wont want to run all those lights. The noise from all the fans, ballasts, etc will be a bit noisy. You will be able to hear it no problem.
If you want it really stealth, get an apt with a 3rd bedroom and use this. This way no one will ever go into that room, the noise is blocked by the door, and so on. 1200watts is usually not what people do when they want things stealth. 1 400watt setup would be fine, but with 3 400watt lights, you are talking about so much space, noise, etc its almost impossible.
So as I said, all of those will work, but none of them are going to be too stealth. The best bet would be a 3rd bedroom, or better yet, don't get a room mate and use the 2nd bedroom for the grow. In my opinion, its a bad idea to grow with a friend unless you're going so big you can't handle it yourself.
Sorry to just go on about the negatives, but I'd rather have some one mad at me for shitting on their ideas than going to jail, getting robbed, etc, because they didn't look at the whole picture.
Good luck,
Bon