im guessing the house has thick walls or something?
have you tried moving the aerial around on the back of the desktop?
by ethernet bridge do you mean a powerline adaptor? if so then all you need to do is get a pair of them, and its a 30 second plug in, turn on, connect the plugs to your router and desktop and away you go.
the adaptors themselves are pretty generic, i run mine from downstairs from my modem, to my room upstairs and connect it to my router.
what i would say is if you are going to buy a set, do so from a shop with a decent return policy, just so in the event that it doesnt work you can always take it back, but from my personal experience it was so simple to get working.