That light is suitable for the space, but it may not quite be powerful enough for four mature female plants. Don't get me wrong, it'll definitely work... but it may not produce the densest buds because the light will have a hard time penetrating beneath the canopy. If you can ventilate the room in question, you may want to think about getting a 400w instead. But, regardless of which system you get, make sure you're able to keep the area cool. You want to keep 'daytime' temperatures below 80F if at all possible. Cool-tubes and air cooled hoods make this much easier.

If you're bound and determined to go with a 250w system, maybe think about paying a little bit extra for a switchable ballast that'll run both MH and HPS. If you only have a choice between one or the other, I'd recommend going with an HPS. Much better spectrum for flowering, and is also fully capable of vegging plants... you'll just need to watch out, because HPS light can cause plants to stretch, especially when they're seedlings.

(Edit: Oops, sorry Stinky... ya beat me to it. You can delete this post if you'd like.)