Here's a little circuit that simplifies interfacing to bipolar
stepper motors. It's similar to a common unipolar design available
on the internet. However, I modified it to use a pair of
MOSFET-based H-bridges. In addition, I added an enable signal so
that the motor windings can be disabled to save power. Since there
are diodes embedded in the transistors, there's no need to add
flyback current protection across the motor windings.
A couple of notes: ORCAD does not explicitly show the power
connections for the logic devices so be sure and connect the
flip-flop and XOR gate packages to +5 and ground. The MOSFETs
specified in this design are surface mount and can handle about
500mA. If you don't want to lay out a printed wiring board, then I
would recommend the use of Surf boards from Captial Advance
(http://www.capitaladvanced.com) these handy devices
let you prototype with SMT devices.
If your motor requires more current then you will have to select
bigger transistors. The threshold voltage of the transistors should
be in the range of two to three volts to guarantee saturation.