if you only need to control the speed of the motor and NOT the direction you can use a simple transistor / diode setup like this :
If you need to control direction you need an H bridge IC, or a dedicated motorcontrol circuit.
By the way if you have access to "electronic waste", old printers are a really good source for both DC motors and steppermotors, and other nice mechanical bits and pieces. I have taken a part lots of printers and have a nice pile of motors. If possible i sometimes also save the powersupply for the printer, so i have something to power the motors with.