not too difficult to set up. as stated earlier, apply for a free dev subscription to get a key. if the plugin is not working at first, test manually like this:

http://api.wunderground.com//api/b94178*****efab/conditions/forecast/alerts/q/Zonnebeke.xml

replace b94178*****efab with your key.
only 10 requests/minute and 500requests/day are allowed if you use the free subscription