I've heard of mains networking (One of our Eletricity companies was trying to give Broadband via the mains!) but I've never seen any kit, just googled a bit and found some nice info:
http://www.reghardware.co.uk/2007/06...owerline_pack/
http://www.maplin.co.uk/Module.aspx?...C=SO&U=strat15
http://www.maplin.co.uk/Module.aspx?...C=SO&U=strat15
Perfect solution, except for the price, I think these will be too expensive for him! I will tell him about them though, they could go back and see if they could swap the Belkin router for one of the mains networking kits though, that would probably be better and he'd get one of those extenders as part of the kit!
Cheers Tip