How old are your plants? If they are the veg stage the general consensus is to run the lights 18-24hrs per day. Personally I do 24, i think more because I do not feel like buying a new timer for my veg lights. If you can run the lights anywhere in that range you will be fine.
For lights how much cash are you working with? A HID setup is excellent choice but I little higher priced. I use CFL's, they seem to work just fine. If you are still new at this I would probably steer you toward CFL's. They are cheap, safe, and easy to modify your setup depending on what the plants need.