Polygon issues!!

Hi there, I''ve got to model a car for my openGL coursework - its gotta be coded so cant use a modelling program. The problem lies in making round wheel arches for the car body. I was wondering if it is possible to subtract a polygon from another. For example, have a rectangular wing and ''take-away'' a circle from it to leave a round ''hole'' in it?? Any help, or advice would be greatly appreciated! Cheers in advance, Paul