Since you're looking at distances upto 400m, the best thing to do is buy a wireless router and set it up with the broadband, putting it near a window facing the other house.
Then, put an access point (with repeater capability) in the window of the other house. When set to repeater mode, this will enable wireless connectivity straight back to the router of the other house
http://www.wi-fiplanet.com/tutorials...le.php/1571601
has a few bits of suggested equipment