I'm also a student...
I started off using an old unipolar driver (compucut) that I got from school on my milling machine. It was fine for the first few weeks but I soon got bored of the extremely low feedrates and I'm sure you would. Unless the machine is very small you need to be looking at higher voltage drivers (about 50V) and bigger stepper motors unless you've been very lucky with the printer. For instance the m542 drivers.

The driver you lined to on eBay is actually only half the driver, it doesn't have the signal processing to convert step/direction signals to the correct sequence to spin the motor. It's effectively just an amplifier. Not much use...

What type of 'thin metal sheets' are you intending to cut? Unless it's very very thin you're going to need a very rigid machine.