Led driver questions
 

I've got 3 drivers sitting around from some led fixtures i destroyed and I'm just wondering if they could be used for a DIY led with 3w bulbs

They are 12v 36w 3000ma

If they are usable would I have to do 3 sets of 4 leds to get the proper voltage/current to them?

drivers
 

divide the watts by 3 to get the amount of leds

Doesn't the voltage and amperage have to be proportionate to the wattage tho?

If they're not dimmable, 3000 mA will fry your LEDs. You could run 3 parallel strings of 4 off of each driver as you said. That'll give you 12V, 1A per set of 4 LEDs. You want to try and keep the wiring of each string roughly the same though. If one of the strings has a different resistence than the others, it's possible that one string could be running over 1000 mA, which can burn out your LED (depending on what type of LED you're using).

Watts=volts x amps
Your idea of running three strings of 4 LEDs might work, depends entirely on your LEDs. Each string in series should total 12v (in your suggestion of 4 LEDs you are implying they would be 3v each), and each string hooked up in parallel contain nothing but 1000ma LEDs. You may have 750ma or 700ma LEDs, in which case you would need 4 strings (4 x 750ma leds would consume all 3000ma but 4 x 700ma leds would end up being a bit overdriven). There are solutions to allow flexibility in these options and excellent explanations on these can be readily found on the net.
Dan