The Linksys bridges are my favorites and incredibly easy to install. Plug them in either building and suddenly both networks are linked. No drivers needed, and there is a web-based set-up.

Do go to the trouble to set up security though. Also, at 200' w/o obstruction, I'd bet you could connect w/o other antenna's. I'm right at 250' through a window and an intermediate neighbors roof. The Linksys units (at least the ones I've used) do have removable whips should you need. The WET54G also supports P.O.E. which could be handy too.