Hold up-- here's the solution:
Using scrap 1x4 lumber cut a board out that is 4 inches longer than the diameter of the hole you need to cover. With a screwgun ready to go at hand, take the board and put it in the hole, behind the drywall so that the board overlaps existing wallboard on both sides. Use the screwgun to put screws through the drywall into the board-- 2 on each end should do it.
now you have a hole in your drywall with wood directly behind it. Cut out a piece of drywall to fit the hole, leaving about a quarter inch on all sides-- no need to be too precise-- and screw this patch piece to the new board.
Now mud it up and make it smooth. Done this way you can have that hole patched in no time.
Method taught to me by a neighbor who has been a professional drywaller for 20+ years.
Last edited by kornkob; 08-28-2008 at 10:23 AM.