pike,
you got mistakes, the servo motors have two typical types which are DC servo and AC servo.
A DC motor is the most popular motor in robotic applications. Servo mechanic structure is just a DC motor and an encoder fixed together.
Servo motor is a close loop motor. You need to use PWM to drive a servo. you may use some chips like: TA7288A, L293, L293D, L298, ...
The motor you say is a Stepping (Step or Stepper) motor. Stepping is a open loop motor, the smallest full step is 0.72 deg/step. However, you may drive it at half step mode, or microstep mode to make it nearly continously run. The suitable chips for stepping may be ULN2003A, ULN2803....
https://www.cs.uiowa.edu/~jones/step
mario,
But normally, for beginner, you should try with simple DC motors.
To drive a small robot, there are many model of wheeled mobile robots. However, you can use NEWT model, which is easy to drive the robot, with 2 active wheels. Active wheels, that is, the wheels are connected to motors. An the 2 wheels are on opposite sides.
At first, you should solve the kinetics, and understand how to drive a robot. There are many simple robot projects, especially on linefollowing. However, my data was lost, and I don't remember the usefull URLs. But you may check in this forum, people discussed much bout it.
You can firstly build a line follower with basic PIC 16F84, it's very easy, and you can build your own IR sensor to detect the line. You need only 2 pins of PIC to detect IR sensor. Try it, and good luck.