clueless wireless question

[Tony Alfrey]

Hi;

The guy that rents our apartment above our garage is a Google geek and 
has just today got a cable modem installed and us less-geek-like 
landlords have cable envy.  So we're trying to figure out how to get a 
wireless network set up.  He uses a Mac with an Apple Airport Extreme 
box that connects to the cable modem.  It is, in essence, a wireless 
modem (I think that's the correct term).  We'd like to continue to use 
the Airport Extreme because it also has a firewall inside that our 
GoogleGeek can configure.  We plugged an external antenna into his 
Airport Extreme to increase signal strength, but still do not have 
quite enough range.  The Airport Extreme has a LAN port on it also.  So 
my question is:

Can I buy a wireless modem that will plug into that LAN port that will 
give us boatloads of unidirectional signal?

If so, then can anyone also suggest a brand of external wireless modem 
that I can plug into my linux box for which there are linux drivers? 
(I'll let my wife struggle with her Windoze laptop by herself ;-)  )

Thanks in advance!!

-- 
Tony Alfrey
tonyalfrey at earthlink.net
"I'd rather be sailing"