The L298 is a bipolar driver... you can make it work with a unipolar motor by ignoring the centre tap connection on the coils and just using the ends. The performance you will get compared to a proper unipolar driver will be reduced because the coil inductance is quadrupled and the coil resistance doubled therefore the torque drop off with speed will be much higher. But that might be ok for your application.
If you're in Europe why not come and visit the UK CNC Community at http://www.mycncuk.com