Thanks for all the helpful advice/info here. Sorry if I confused a little, I didn't want to buy the wireless router I used as an example (actually it is out of stock at the outlet I would have used), I just wanted to understand the relevance of OS requirements when listed in router specs. On balance, it is probably something to do with router setup files being either on CD/DVD or for web download only having been tested on later OSs. As I have a Win8 machine to do the setup I won't worry about using WinXP machines through the new router, it will be here on Monday.
Just for info I decided to test the various ways of getting the signals around the property. I have 6 Powerline adaptors, not the latest and greatest generation but serviceable. Several are in use getting internet access to a hard disk freeview recorder, getting access to a couple of networked printers scattered about and, initially, getting my Netgear wireless router connected to the incoming router. When I only got 3.6Mbs through the Netgear router I assumed that the Powerline adaptor link was not working well as it is across different circuits/fuses. When I replaced the Powerline adaptors with a 15 meter ethernet cable I was a little surprised to find that it did nothing to improve the data rate through the Netgear. Today, I tried using the Powerline adaptors to connect the incoming router to the location of the Netgear but plugged the Powerline directly into a fast laptop. The speedtest came in at 12Mbs, not too bad but a long way short of the 37Mbs I get using the cable to do the link. The Powerline adaptors won't work from the house ring out to my external workshop which is powered from the garage ring circuit from the main fusebox. Now I understand the speeds of data I can get through the various links I can figure out the best way of getting everything connected to get the speeds where they are needed.