I've always wanted to setup my own long range wireless LAN, but have never had the need
(and before you ask boxer you are too far away to share my ADSL
) Sounds like a very interesting project!
You may want to do a Google search, I found
this in a few minutes, there is loads of info out there.
I'm sure that 4 AP's would do the trick, but how much cooler is a MESH wireless lan shared out to your mates. I think tfabris houses some gear for one of these networks, Tony ???
I do run a mini version of what you are trying to do. I have 2 D-Link DWL-1500 Wireless Bridges, this extends my network into the kitchen to feed my Rio Reciever and acts as a repeater to extend the range for my laptop (it says in the manual this souldn't work, but it does???). You do need directional antennas at each point of the connection, so you will need 4.
The danger in using WAP's is that you are extending the schools network out into the community, you need to consider what security you are going to set up, a firewall at the school end would be cool.
Also, would there be much of a lag for your mate at 2.5km from the T1???
Mmm, really wish I had a project like this to have a stab at!!!
Cheers, goodluck, keep us posted on your progress.
Cris.