You just need a pair of powerline plugs. Plug one into the mains near your desktop PC and run an ethernet cable between them. Plug the other one into the mains near the router and run another ethernet cable. It then behaves as if you have a direct ethernet connection from PC to router, without any of the hassles of wireless. I'm using the ones that came with my BT Vision box, but I have also used Advent brand powerlines which also worked brilliantly.
I originally used a usb wifi adapter but had no end of trouble but now I get no loss of connection at all.
Hope this helps.