I checked your ebay source. 12 volts at 6 Watts means 500 ma of current is needed (MAX). You have 6 modules with 5 leds each so thats 30 leds. 0.2 Watts per led. It would seem from the pictures that the leds are wired in parralel, meaning that they all get 12 volts and fight over amps. So voltage dropping isn't a problem. 0.2 watts/12volts gets you 16mA.
So if you're going to power all six, then you need 12 volts at no more than 500ma. If you're going to power one module, you need 12 volts at no more than 83 mA. If you're going to power one LED you need 12 volts at no more than 16mA.
EDIT: see next post.
-Catcher