1) Go to www.wunderground.com
2) In the search box, type your zip code, or the city that you are looking for.
3) On the city forecast page, click 'add this sticker to your homepage'.
If the city isn't in the US, then it will say 'add a wundergraphic to your homepage'.
4) Follow the instructions at the top of the page, if you want the banner in metric, choose that link at the top of the page. When you select a banner click on it and copy the html code to your page.