(Instructions for installing the custom madwifi can be found here: [http://forum.eeeuser.com/viewtopic.php?pid=47421#p47421])

To configure for wifi without encryption (not advised):

(File: /etc/network/interfaces)
auto ath0
iface ath0 inet dhcp
pre-up ifconfig ath0 up
pre-up iwconfig ath0 essid "router ID"

To configure for wifi with WPA(2)-PSK encryption, you have to "aptitude install wpasupplicant". Open a text file and paste this and save it as /etc/wpa_supplicant/wpa_supplicant.conf:

ctrl_interface=/var/run/wpa_supplicant
ctrl_interface_group=0

ap_scan=1
fast_reauth=1
eapol_version=1

network={
        ssid="ROUTER ID"
        psk="your password"
        priority=5
}

Then edit /etc/network/interfaces with this:

auto ath0
iface ath0 inet dhcp
wpa-driver wext
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

Reboot and you have wifi :)