i'd like to use a few of 254 cable connections on a private tv cable network to
link windows and mac computers for file sharing. i believe i need a cable modem
at each location and might be able to use vpn. there is already an internet feed
on the network along with television signals.

i know now to install vpn.
what kind of cable modems do i need?
will vpn work in this setting?
am i asking the right questions?