Abstract: A computer network is installed in a building such as a hotel having a plurality of rooms. The building has a preexisting electrical wiring grid to distribute electrical power to the rooms. At least one power line injector is operatively connected between a server computer and the electrical wiring grid to transfer data therebetween. The data is thus transmitted and received across the electrical wiring grid via a modulated carrier. A plurality of power line modems are respectively installed in the rooms of the building and are connected to the electrical wiring grid to selectively transmit and receive the data. In addition, a plurality of end user computers are respectively associated with the power line modems.