I have some NEMA 17 motors that I've tested lightly with them. They seem to work, but I haven't tried it under a real load. These are also 400-step motors (most NEMA 17s I've seen are 200 step), so that may be a factor. Apparently, the NEMA standards refer only to the dimensions of the motor's case, and what's inside could vary pretty widely, so they may be able to drive some NEMA 17s but not others. Mine are rated for .67A/phase for bipolar operation (this appears to be lower than most), so they should be fine. If there's a model number on your motors, you should search for a datasheet. If you don't need microstepping, a chip like the A3982 on the makerbot driver board should be a better choice.