One of the universities I visited used old coax cable runs in their dorms as wireless antennas.
The jist of how to do it was to attach a low power power amp to the output of a typical router with support for external antenna. Then wire the gained end of the power amp to the coaxial cable. You have to use a second power amp (or the other half if has two channels) to gain the return from another coax cable to receive signals. The setup isn't exactly simple.... but it works fairly well if the house gets poor reception otherwise.
In my univeristy example, they used one floor's cabling for transmit and the next floor for receive, repeated until out of floors.