ah, your only doing two plants?
get yourself one of the 150watt HPS lamps dude.. they're really cheap but they're extremely reliable. I think I paid like 60-80 bucks per light. Comes with enclosed ballast AND the 150watt HPS bulb. Can't hardly beat that man. Thats how my setup was.. when I first started. I had just the one 150watt HPS.. but I also had 4 150watt CFL bulbs (2 per plant) for side lighting. Setup works just fine for what I need.. I'll probably upgrade and get two 250's this coming summer.. but until then, I use what I just posted and it works great for what I need.
good luck to ya.
peace.