Flat screen TV mounting over a fireplace?

Ok I live in a condo that has a funny layout. The fireplace is kind of in a corner and above it is the "media" area. There is a whole cut out in the wall where a normal old school type tv fits and a small shelf where the dvd player sits. I'm in the market for a flat screen...possibly plasma tv. I have measured it and the actual hole is 35 inches (corner to corner) and 39 1/2 inches from the top of the wall down to where the dvd shelf is built in. I wanna mount the tv brackets on the outside of the hole area and situate the tv there. I don't want to see the hole, I don't want to have another hole drilled in the wall to run cables/wires, I don't want to have to purchase a stand and go through the trouble of rearranging the furniture for that. Is this possible. I don't see why not. I seen a mounting bracket at best buy that will expand up to 80 inches. I have used the stud finder and there are studs on both sides of the tv hole. Why would this be a bad idea? Shouldn't it be possible? Also....is there any store that offers free installation? Best buy said they would install it for 349.00....which I think is a bit much since the tv itself is gonna cost around a grand, plus 250 for the bracket.