PCW would not be my choice, especially if you are not certain what you want. You would be better going to a small independent shop where the owner/assistant will know what you want and make a recommendation. Whatever you do don't waste your money on an N class adapter, it will be no better than a G and will be twice the price. An N adapter needs an N router which you don't have. Also don't be fobbed of with a B, this is old stock and will be too slow.

I think most here would recommend you use Homeplugs, rather than wireless, they are faster and more stable. This will give you an idea of what I mean -
HomePlug AV | Broadbandbuyer.co.uk