firewalls ...

[pinniped <cirilo_bernardo@yahoo.com>]

Firewalls only have a little to do with it - but you can essentially set up the equivalent of a VPN without using VPN software.  The only down side is that every user has to be authenticated.  But your AP can be completely open - and yet unauthorized users can't do anything except 'jam' your communications - something they can easily do even with a secured wireless net.  There are documents out on the net on how to set up an AP like this - it's been done a few years ago.