[Razer]

another simple way to do it is make a flat rectangle. Then make an elipse above the rectangle (say like a ft or more) then high light both and click create surface. Then will make a surface over everything. Now go to object mode and select the area in the mildde of your object that was made when you clicked create surface.

hide it and delete whats ont he screen. Now unhide what you made and go to vertices mode and highlight the area where the rectangle was and click remove surface. do the same for where the elipse was and click remove surface. Now you have a rectangle with a round hole in it. Just highliight the model and drag from the center of the highlight box and flatten it and your done.