radius+ wireless

[Gaspar de Elías <gaspar.delias () gmail com>]

hello
I'm an isp, and i'm providing internet to my customers via wireless,
authenticating with a radius server on freeBSD. My question is the
folowing: Can somebody sniff the wireless conections, crack WEP
alghoritm, and cheat his mac and ip addresses in order to steal
information from one of my customers?
A friend told me that doing this is incredibly easy, so i'm investigating. 
What should i implement to make my wireless lan more secure?


-- 
Gaspar de Elías