If he already has a wireless router which I am assuming he has, then he will still have the option of being able to connect laptops, PC's & consoles wireless. It's just that homeplug will allow you to get a better quality of service by allowing him to connect his lappy/PS3/Xbox by hardwire through his mains electric.
You won't need to update/buy anything new (just the homeplug kit).
What router does he currently have?
These are quite cheap. £19 a plug -
FlaVes85 - HomePlug - 85Mbps. 3 pinned UK plugs, works with any access point and router. 
That's a £38 solution for networking through your mains electric. Now compare that to buying a new N router which can set you back £70.00+ notes and then a N adapter which can set you back a further £40.00+ notes, I'd say that the homeplug option is a bargain.