Four shop flourescent lights should do the trick, cost you about 80 bucks and you can just set them on their end one on each corner, being 4 ft tall they should fit right in. Also, go to the dollar store, you can get reflective window visors for cars for a buck, they work GREAT in a grow room. Drop four of them over the sides and your entire closet will be reflective. Still if you just had a window to put them in they would do a lot better then they are.

A lot of people don't think you can grow with flourescents but my friend grew two full term plants in his closet using 8 of the old fashioned 22W circular lights. The bud smoked just fine, his yeild wasn't great but only took 4 months from seed to harvest, I've also seen this done in a Phototron.