Most articles make this out to be much more complicated than it needs to be. First, make sure you have wpa_supplicant. On Archlinux:
$ sudo pacman -S wpa_supplicant
You will need to add your network definition to wpa_supplicant.conf:
# wpa_passphrase YOUR_SSID YOUR_PASSPHRASE >> /etc/wpa_supplicant.conf
Finally, create a script to bring the interface up. I put mine in ~/scripts/wireless.sh:
#!/bin/sh sudo pkill wpa_supplicant sudo pkill dhcpcd sudo ifconfig wlan0 up sudo iwconfig wlan0 essid YOUR_SSID sudo wpa_supplicant -B -Dwext -i wlan0 -c /etc/wpa_supplicant.conf sudo dhcpcd wlan0
Change your ssid and interface accordingly. Run that script to connect!