My config looks like this:
/etc/network/interfaces
auto wlan0
iface wlan0 inet dhcp
wireless_mode managed
wireless_essid <ssid>
wpa-driver wext
wpa-conf /etc/wpa_supplicant.conf
/etc/wpa_supplicant.conf
ctrl_interface=/var/run/wpa_supplicant
ctrl_interface_group=0
update_config=1
network={
ssid="<ssid>"
psk=<encoded_passphrase>
}
Does "ifup wlan0" show any messages?