monitoring multiple camera

Hello,
I am doing a project on monitoring multiple cameras.
I want to monitor 4 cameras video in my PC.and I want to control the direction of each camera with pan and tilt mechanism employing stepper motors.so, i need to control the 8 stepper motors and monitor 4 video from cameras. And I want to perform all these things with single USB port. So I need some help for the hardware. Because I want to make my own application. Can anyone help me for the hardware for monitoring multiple cameras from single USB port?

With Regards,
Vmax.