Gotta disagree with tom, if you've only got 3 feet height to use you're gonna have problems with a hps, they've gotta be positioned further away from the plants than cfl's because of the heat they produce and you really don't wanna have 8-12" of your height wasted, with cfl's you'll probably have to allow 7" for fixing your lights and leaving a little space to the top of your plants, 8" for your pots, that leaves you 21" for your fully grown plant, which is kinda small but will still give you some decent bud, think about using a hps and having to reduce it's size by another 8-12" your gonna be left with only around a foot for your plant! And because you'd have to force flower so early it wouldn't be mature enuff to produce strong buds anyway and a 12" plant ain't gonna use 250 watts of hps light, it's just gonna be wasted. Get some cfls i'd say about 100 watts worth!
Good luck