Although the specification for that stepper says 12-24v, the current rating is 2.5A per phase and the resistance per phase is only 1 ohm. So the maximum steady voltage you may put across a winding when it is not stepping is 2.5v. The 12 or 24V only applies when it is stepping very fast, it's not safe to put anything more than 2.5v across it unless you have current limiting in place. If you ran it from 12v without any current limiting, it would take around 10A, which is why your motor drivers fried. Note the caption "Constant current driver" in the graph on the datasheet.
My immediate advice is to check all the wiring carefully, run from a lower voltage at first instance (minimum is 7V), and monitor the current (the Easy Driver can do 750mA or so to the motor). Only if it behaves as expected do you ramp up the voltage. No-one who has ever developed motor drivers has ever run at full voltage and power in their first test (something always explodes).The real solution will be to use a beefy chopper driver that can handle 2.5A such as the L6208, otherwise you'll never get much torque out of the motor.
can anyone point me in the direction of a good resource to learn how to take one of those and then build a board?
due to the lack of heatsinking
It is very much worth it to have some TO-220 and some DIP heat sinks and some thermal grease laying around. Buying a few of each, plus a syringe of thermal compound (typically found for CPU overclocking) should cost you less than $20, and will make some designs possible that otherwise would be a total pain.Also, it's worth it to go for a few dollars for the "big" sinks -- the small, 25-cent flanges don't dissipate enough extra heat to be real problem solvers except in certain marginal cases.
DIP heatsinks are not very effective. The problem is the thick layer of plastic between the chip and the heatsink. DIP chips that are intended to dissipate much power are designed to transfer heat to the ground legs or tabs of the chip, which can be soldered to areas of copper on a PCB. You won't achieve the same power dissipation capability with a stick-on heatsink.