Hi, well 20W aint gonna get you far, you can grow with flurescent bulbs, I think it takes longer though... stuff those halogen light, they are a complete waste of time.
HPS/HID is the way to go...

you saidl.... "Now..... I HAVE got 3 250w metal halide bulbs (twin ended)"

Is that just the bulb or the whole kit?... if so your need a ballast & a reflector.

I buy all my stuff from http://hydroponics-hydroponics.com/ quite cheap.

hope this helps... dude0