An LM324 is not the right tool for the job. Stepper motors need "CURRENT" and an LM324 can only provide "current". You need a motor driver (see our Rugged Motor Driver or one of the many other Arduino motor drivers out there).
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
Not that I know of. That's a lot of connections, and a lot of inputs too. To handle 10 stepper motors, assuming a simple step/direction interface for each one (never mind an enable pin for PWM control), you'd need 20 inputs (unless you did something serially using SPI or I2C). Well, 20 inputs is the entire set of I/O's for an Arduino.