Wifi

NetworkManager tends to get in the way... big time. Don't forget to kill him.

WEP

stop network-manager
ifconfig wlan0 down
iwconfig wlan0 essid my_network
iwconfig wlan0 key s:my_passphrase
iwconfig wlan0 mode managed
ifconfig wlan0 up
dhclient -v wlan0

Alternatively you can specify the hex value for the key:

iwconfig wlan0 key ...

WPA2

This is untested, but something like this might work:

stop network-manager
ifconfig wlan0 down
iwconfig wlan0 essid my_network
wpa_passphrase my_network my_passphrase > wpa_supp.conf
killall wpa_supplicant
wpa_supplicant -B -Dwext -iwlan0 -cwpa_supp.conf
dhclient wlan0