Thank you, Brian. Thank you, Bill.
That X10 USB CM15A seems to be what I want/need, I guess - judging other articles I went through on the subject. So, correct me if I'm wrong: if I plug the PC to the CM15A, then if I plug that to the power, I can send and receive X10 signals that are travelling through powerlines (of course, provided that I have at least one X10 device plugged in somewhere in the house).
I'm assuming that I would, then, have to start buying those X10 devices (are these what you call "modules"?) to put between appliances and the powerline. So, in my mind, these would be physically different for light-bulbs than those that plug into outlets (?).
I'm also assuming that some of the appliances may be X10-capable already (?), and that I would have to watch for this when buying them, correct? For example, if I want to control a surveillance camera attached to the wall and plugged into an outlet, I would have to either buy a camera that can understand X10 signals or buy a module that is capable of controlling that camera - is that correct? I guess controlling lights should be simple: on, off and perhaps dimming - so, I'd need a module that can do this and put it before the bulb somewhere, correct?
Thanks a lot for taking time to read and to answer my questions.