I just installed Ubuntu Server on a spare computer with a broken graphic card, and I needed to setup my wifi.
I thought No problem, I've done it before from the command line, in Arch Linux., only the steps I had to take in Arch Linux didn't work in Ubuntu Server (that's odd, wasn't Ubuntu supposed to be so much more user-friendly? :/).
This is what I'd normally do:

ip link set wlan0 up
wpa_passphrase <ESSID> <WPA KEY> > /etc/wpa_supplicant.conf
wpa_supplicant -B -Dwext -i wlan0 -c /etc/wpa_supplicant.conf
dhcpcd wlan0

Only at the wpa_supplicant I get some strane message:

ioctl[SIOCSIWENCODEEXT]: Invalid argument
ioctl[SIOCSIWENCODEEXT]: Invalid argument

And if I try to run dhcpcd then (which I manually installed, as it didn't come preinstalled with Ubuntu Server), it times out.

Help on how to do it would be much appreciated.

My wireless driver is iwl3945.