I'm not sure how active they are in your area but you might want to
check out IrishWan, http://www.irishwan.org/ who organise community
wireless lan links.
I have been part of the Dublin branch and it has been quite successful,
as a quick look at the map will show. http://www.dublinwan.org/map.php
The guys on there can guide you with what you need and how to do it, but
yes basically you would need an omni directional antenna, and then users
will point directional antennas at that.
There are a number of gotchas, the omni needs to be high enough to have
good line of sight, trees will cause interference and also TV senders
will interfere with your signal, but other than that it should be easy
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