What you need is the "HD26200" from "HD Communications". It costs US$318, an extends your WiFi range for up to 5 Miles.

The only requirement is that you have line-of-sight between the two end-points. If you do, all you do is connect on of these boxes on your friend's end, and then another in your home, and you're set.

See this link for details: http://www.businesswire.com/portal/site/home/permalink/?ndmViewId=news_view&newsId=20080521005391&newsLang=en