igThemer doesn't let you create themes with multiple scenes, but it hosts your theme so you can share it with your friends or submit it to iGoogle's directory. Regardless of the way you create a theme, an easy way to preview it is to use this URL:
http://www.google.com/ig?skin=SKIN_URL
(replace SKIN_URL with the location of your theme's XML file)
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An even cooler solution lets you edit the theme directly in iGoogle and see the changes in real-time. Just go to iGoogle, copy the code below and paste it in the address bar (you could also bookmark the script):
javascript:var s=document.createElement('script');s.id="igteid"; s.type="text/javascript";s.src= "http://igoogle-theme-editor.googlecode.com/svn/" +"trunk/iGoogleThemeEditor/dist/ige.js?lang=en&" +new Date().getTime(); document.body.appendChild(s);void(0);
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{ The first screenshot is based on the photo Colourful life, licensed as Creative Commons by BlueSunFlower. }