Thanks for the replies.
The set up is that we have a 10Mb cable broadband coming into the router (DIR-615) and my computer is connected to the router by ethernet cables. He rarely needs to transfer files to me, so that's not really an issue. I understand that with 10Mb coming in, the N spec connection between his laptop and the router won't speed this up. So data transfer and internet speed aren't really issues. Although I'd like a network storage box, I can't see that happening any time soon.
His niggle is that he claims he has a poor signal in his room, but the router says he has 80%+ signal, and windows shows 4 bars, so I don't think this is an issue, but was hoping that N spec for him might at least stop him whining! The only other issue is that when the kids are downloading stuff, or uploading things it slows everybody's access down. I'm thinking that this might be a combination of mostly 10Mb connection, wireless G plus some elderly pc's.
I'm thinking now that unless I upgrade the cable broadband to 50Mb (not gonna happen currently), or have a network storage box, there is nothing to be currently gained by upgrading to wireless N (apart from his lordship getting a marginally better signal maybe). I guess that I will switch everybody to N spec adaptors when theirs die, or I come into some money and can upgrade ny broadband etc.
Thanks for helping my clarify things!