How do you know it does not exist? Most of the time it is installed but the
user has not set up a connection.

The system does not even indicate that it is installed, let alone give me a
chance to set up a connection. One related question: I am contemplating
getting mobile broadband as an interim internet solution. Will mythbuntu work
with that? If so, how do I go about using it? Please feel free to refer me to
appropriate documentation if thee is any, so that I don't take up too much of
your time--

Have you done all the updates and also run Hardware Drivers update ?
Given your 'spotty' internet connectivity you may not have had a full
run at updating yet. Since Ubuntu 10.04 the Broadcom chipset Wi-Fi is
detected by the hardware driver update and once that's done it works
fine so there's no need to manually compile anything.