I had the same result until I added the channel number and name to my interfaces file. It looks like you need to add the name and wireless channel you are using and change the underscores with dashes. Here is my interfaces entry:
neuromancer:/home/hank# cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
# auto eth0
# iface eth0 inet dhcp
# name Ethernet LAN card
# The wireless network interface Netgear WG-311T
auto ath0
iface ath0 inet dhcp
name ath0
wireless-essid ********
wireless-key **************************
wireless-channel 10
My card is listed as ath0 because I am using madwifi drivers.
I hope this helps.