Hi, Some info about this type driver board here:
http://arduino-info.wikispaces.com/MotorDrivers
and the chip info here:
http://arduino-info.wikispaces.com/L298N-DataSheet
You can't drive this board with only direction and step; that takes more logic or a special chip like the EasyDriver.
You CAN reduce the number of pins to one for each motor winding (two total) IF you will only single-step the stepper. In that case you need to add an external Inverter chip between each set of two motor driver pins so that those pins are always opposite polarity.
Typically you'd use a 74HC14 or 74LS14 or equivalent "Hex Inverter" chip (Which has 'hex' that is 6 inverters in a package).
You can get a EasyDriver here: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=280
DISCLAIMER: Mentioned stuff from my own shop...!