From wiki.network-crawler.de

For Gentoo

emerge wireless-tools
echo "net-wireless/madwifi-driver ~x86" >> /etc/portage/package.keywords
echo "net-wireless/madwifi-tools ~x86" >> /etc/portage/package.keywords
emerge madwifi-driver madwifi-tools
modprobe ath_pci

For Debian

add to your /etc/apt/sources.list:

deb ftp://debian.marlow.dk sid madwifi
deb-src ftp://debian.marlow.dk sid madwifi

apt-get update
apt-get install kernel-source-2.6.8 kernel-package madwifi-source madwifi-tools debhelper sysutils
apt-get source madwifi

cd /usr/src
tar -xjvf kernel-source-2.6.8.tar.bz2
cd kernel-source-2.6.8
cp /boot/config-2.6.8-2-686 .config
make-kpkg --append-to-version "-2-686" --revision 2.6.8 --config old configure --arch i386

cd madwifi-1.x

I used madwifi-1.7 and there is a bug:
edit debian/rules and change

CVSHOME=cvs -z3 -d:pserver:anonymous@madwifi.cvs.sourceforge.net:/cvsroot/madwifi co -P madwifi

dpkg-buildpackage
cd ..
dpkg -i madwifi-source_20050212_all.deb
dpkg -i madwifi-tools_20050212_i386.deb

cd /usr/src/
tar -xzvf madwifi.tar.gz
cd kernel-source-2.6.8
make-kpkg --append-to-version "-2-686" --revision 2.6.8 --added-modules madwifi modules_image
dpkg -i /usr/src/madwifi-module-2.6.8-2-686_20050212-1-onoe+2.6.8_i386.deb
update-modules
modprobe ath_pci