Have an all-in-one modem/router/wifi point; what do I need to add to extend wired/wifi network?

"Run a single ethernet cable to the upstairs, then put a switch on the end. This will give you 4 (assuming you get a cheap 5 port switch) ports upstairs to do with as you wish. If you then want wifi upstairs you can add a seperate access point hanging off the switch.
You could, if you only want a decent wifi signal upstairs, run a single cat5 upstairs and put a stand alone access point on the end. If you want a cheap, G only access point then I suggest the tp-link wa501g, available from diskdepot for not very much.
Lastly, powerline networking will work through your consumer unit, so the fact it is a seperate ring main shouldn't matter, only if they are seperate meters will it probably not work."