Some questions about lighting for small grow

Hi, I'm just finishing off my first ever grow, under CFLs. I really enjoyed and want to do it again using better lighting. Here's what I'm looking at:

http://www.1000bulbs.com/product/4980/LU0250-0001.html bulb
http://www.1000bulbs.com/product/6007/BS-LU0250MT.html ballast

Is this a good choice for a small closet grow, two or three plants hoping for 4 or 5 ounces all up?

Do I even need a ballast? I mean, does the bulb screw into the ballast or what? If not, is a ballast necessary for 250watts? Sorry if that's a stupid question, I'm just not sure how to research it... And is an HPS always in the 2700k spectrum?

Basically, if I buy the two products linked above (and a fan and reflector) would I have everything i need to harvest 4 or 5 ounces (all else being equal)?

Thanks for any help.

yes, you need the ballast. also need a reflector and a mogel socket and a some wire to attach the light to the socket and a male plug.depending on where you plan to place it, a metal can (w/ vent holes)to mount it in would be a good idea.
general rule of thumb is to expect 1/2 to 1 gram per watt so 4-5 oz is a good expectation until you dial in your room & get more experience.