is there a program that will show me any/all users using my bandwidth at random?
Network Magic. Well worth it IMO. makes many tasks very 'newbie friendly' and has a network map that shows when people logon, name of the device, and you can even mark them as intruders etc. I'm still using the free trial, which is very limited but the full version is nice.
if you have norton you can see who is on each port of the router ( more user friendly). other protections may have the same stuff. or you can go into your router and look at the port activity and start matching devices.