I use the following script to easily configure my wlan connexions.

It can be used in 3 ways :

1 - no parameters : it is going to detect automatically available wlan and connect me automatically to the first know one as found in /etc/sysconfig/network/wlan/.

2 - eth0 : deactivates wlan0 and activate eth0

3 - conf name : it directly applies a conf whose name is found in /etc/sysconfig/network/wlan/

I have added to my K menu the following 3 entries :
- iwautoconfig eth0
- iwautoconfig
- iwautoconfig barnucopia
To make switching network easier.

I use it on Suse Linux Pro 9.3 with great success...

#!/bin/bash
#
# Usage:  iwautoconfig [eth0|wlanconfname]
# 
# Automatically configures wlan based on the findings of
# known networks compared to available networks.
# Use param eth0 to disable your wlan interface and 
# enable eth0.  If you specify a wlanconfname, it must be
# the name of a valid conf file that will be used without
# searching for it.
#
# You need to have a dir specified by WLAN that contains
# various valid config file.  Name of the file should be
# the essid of the network it applies to.  To add a new
# network, configure it using yast, then copy the file
# /etc/sysconfig/network/ifcfg-{interface} to the wlan dir.
# If no network seems to match, the config file named 
# 'default' will be used.
#
# Note that the user executing this command must be 
# configured as a sudoer...
# 
# Author : nicolas@barcet.com

##### CONSTANTS :
# WLAN : Specify the dir where valid config are stored
WLAN=/etc/sysconfig/network/wlan/

# NETWORK : Place here the root name of the config file
NETWORK=/etc/sysconfig/network/ifcfg-

# INTERFACE : name of the interface to be configured
INTERFACE=wlan0


CONFDIR=$(sudo ls $WLAN)  # Get list of valid configurations
ESSID=""

if [[ $1 != "eth0" ]]; then
	sudo /sbin/ifdown eth0 &> /dev/null
	sudo /usr/sbin/iwlist wlan0 scanning > /tmp/iwlist.tmp # Retrieve list of advertised wlan

	if [[ $1 != "" ]]; then
		ESSID=$1
	else	
		# search in list of available conf a net that is available
		for NN in $CONFDIR ; do
			if [[ `cat /tmp/iwlist.tmp | grep $NN`  != "" ]]; then 
				ESSID=$NN
				break;
			fi;
		done
	fi;
	
	# if we did not find any valid net, use default
	if [[ $ESSID == "" ]]; then 
		ESSID=default
	fi;
	
	#copy the good conf to make is active
	sudo cp $WLAN$ESSID $NETWORK$INTERFACE

	#set iwconfig appropriately
	source $WLAN$ESSID # Read the var values from the file
	if [[ $WIRELESS_AUTH_MODE == open ]]; then 
		WIRELESS_KEY_0='off' 
	fi;
	sudo iwconfig $INTERFACE rate $WIRELESS_BITRATE
	sudo iwconfig $INTERFACE mode $WIRELESS_MODE
	sudo iwconfig $INTERFACE enc $WIRELESS_KEY_0
	sudo iwconfig $INTERFACE essid $WIRELESS_ESSID
	sudo iwconfig $INTERFACE commit
	
	#force full reload if conf has changed from before
	if [[ $ESSID != `iwgetid wlan0 -s -r` ]]; then
		echo Found : $WIRELESS_ESSID - Forcing conf reload...
		sudo /sbin/ifdown $INTERFACE &> /dev/null
		sudo /sbin/ifup $INTERFACE &> /dev/null
	else
		echo Found : $WIRELESS_ESSID - No Change
		sudo /sbin/ifup $INTERFACE &> /dev/null
	fi;
	
	#set iwconfig again !!! Just to make sure
	sudo iwconfig $INTERFACE rate $WIRELESS_BITRATE
	sudo iwconfig $INTERFACE mode $WIRELESS_MODE
	sudo iwconfig $INTERFACE enc $WIRELESS_KEY_0
	sudo iwconfig $INTERFACE essid $WIRELESS_ESSID
	sudo iwconfig $INTERFACE commit
	
	sleep 10
	
	#Are we now really connected ?
	NEWESSID=`iwgetid $INTERFACE -s -r`
	if [[ $NEWESSID == "" ]]; then
		echo ERROR !! Not connected to anything...
		echo 'Available nets follows :'
		grep ESSID /tmp/iwlist.tmp
                kdialog --passivepopup "ERROR !! Not connected to anything..." 30 &> /dev/null &
	else
		echo ---------------------------------------
		echo Now connected to $NEWESSID
		echo ---------------------------------------
                kdialog --passivepopup "Now connected to $NEWESSID" 30 &> /dev/null &
	fi;
	rm /tmp/iwlist.tmp
else
	#We want to switch back to eth0
	sudo /sbin/ifdown $INTERFACE &> /dev/null
	sudo /sbin/ifup eth0 &> /dev/null
fi;