Newby: Wireless recomendations for local internet sharing?

Here's the deal.

Broadband is too expensive in Aussie land! Especially in the country! Even
in major country cities. Small download capabilities and yet unlimited is
just that little bit out of reach cost wise for most people! Yet unlimited
downloads really only cost about $20-30 more per month.

So , I want to install broadband isp unlimited at 256k adsl here at my
house. I want an adsl modem/4 port switch to connect local (in my house 3
computers.)

Her is the part i am really seeking advice on. Using either some sort of
adsl modem/4port sw/802.11 wireless unit to connect to local outside
antenna to share that connection to a local friend.

At this point lets stick to the physical details. His location is a little
over 2.5km away. Not exactly line of site but the top of my tv antenna pole
on the roof (approx 45' above ground and a 20' pole at his house ) would be
sort of skimming line of site.

As far as adsl, the local network switch, firewall I seem to comprehend all
that ok but have no experience at wireless networking.

Can i use the adsl,hub,802.11 device which would need an external antenna ,
up a pole (no shortage of ldf4-50 or even 5-50 if req) up to a high gain
antenna 20+db and say 15-18db gain at his end, where he has a pci wireless
modem card get useable results or must we go for something up the pole to
reduce cable losses? Am i then looking at an access point? Or can i use
some sort of ethernet wireless modem up the pole in a box, cat5 down the
pole to the network hub and it becomes part of the network?

Security for wireless also seems rather low or non existent too. Do i need
wap, wep or karlnet? If his wireless networking card (being more centrally
located in town) hears more of these units then will that severely reduce
his performance? Even though i have tried some research i am not really
getting very far. The first few steps with anything new seem so wobbly and
strange!

I am a ham (not very active these days) , and work with commercial 2.4gig
links for commercial video linking in my job, can build antenna's, and have
30 years electronic servicing. But when it comes to wireless networking i
have zero experience.

any comments or suggestions or web site to get more information would be
appreciated.

Thank you kindly,

minsik@"NOSPAM"4u.net