Hi Prart,
Like you said, the acquisition from your USB camera could be handled by NI IMAQ for USB. This does require NI Vision.
Since it sounds like you are attempting to do this without Vision or any other tools, you will probably need to interact with your camera's driver through dll calls. Unfortunately this may vary from camera to camera and will probably be pretty tough. I would recommend that you start by finding out more information about how to communicate with and control your USB camera.
Good luck!
Robert