well, yeah, that's the general idea, you need two antenna, and you need to find a place where you can get the internet connection. But before you do this, you need to understand that some isp might have a problems with the internet connection sharing part. if your going to spend time and money on this, make sure your allowed to do it. If you have a good line of sight, a 20km point-to-point link is not impossible, some of Ubiquity Networks solutions are rated for 50km+... But personally, i would not go that far, the link would be slow and unstable. If you can find a few folks that have the same problem, you might be able to build a small community wireless isp, a few smaller link instead of one big one might be preferable. try asking in the wisp forum for more specific questions: »Wireless Service Providers
also, look at the menu located at the bottom left area of the ubnt.ca web site, click on link configurator. It will help you make sense of what's possible. keep in mind that there is no guarantee a link is gonna work even if the link configurator says it will.