Extending range of WiFi links?

I have a big old solid panel C Band 8 ft diameter dish which is not doing
much these days. I live just outside of any areas from which I can get high
speed Internet and we were wondering if it might be possible to extend the
range of standard lap top computers to pick up signals from the nearby (15km
or so) town. I could repoint the big dish and fit it with a suitable
receive/transmit antenna and, presumably, increase gain quite a bit for both
send and receive signals. Do any of you good folks have any ideas about
doing this, in particular what sort of range extension might one expect. I
know that there are limits on power which can be transmitted and this would
limit what could be done but I am only just outside the range of existing
systems so it might be possible. Any links or advice would be happily
received.
My son was recently in the local city and found, to his surprise, that
there were lots of signals found by his new lap top which were open for use
by anyone. I assume this is an error on the part of the subscribers. I
haven't seen any comments about this on the newsgroups I usually check and
wonder how common it is.
Alan C




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