This is what my /etc/network/interfaces looks like

auto lo wlan0
iface lo inet loopback

allow-hotplug wlan0




iface wlan0 inet dhcp
wireless_mode managed
wireless_rate 54M auto
wireless_channel 11
wireless_essid XXXXXXXX
wireless_key XXXXXXXXXXXXXX
post-up route add default gateway 192.168.0.1

It now starts everytime!!