Buying a home with a "Plasma Pre-Wiring" done?

I am buying a house that has "plasma pre wiring" done, along with surround speakers prewired also. From what the builder told me, the components will go against a wall, while the flat screen goes above the fireplace. The wall plates only have coax cables and the wiring is in the walls already (just running through the studs). He wasn't very clear how it all works. Does anyone know if I need to run HDMI cables through the walls to replace the coax cables or what? This is my first home theater, and I have a 42" LCD flat panel, blue ray disc player and DirecTV HD receiver. Can anyone help?