Below are the steps mentioned on a thread to resolve same issue on RHEL 5.
1- Install and update RedHat 5
2- Build and install madwifi from source
3- ifconfig ath0 up
4- Lauch KDE's wifi application
My mistake was to think that RedHat would have created a wifi0 device. In fact, I needed to use ath0.
Have look at below mentioned thread: