From their site: iGoogle provides users with a personalized view of the web. You can leverage the themes API and tools to build themes about outer space, cartoons, dogs, or anything you can dream up, helping to further personalize iGoogle. This is your chance to redesign the Google homepage for tens of millions of iGoogle users. Your theme can modify the header and footer images, text colors, link colors, gadget frames, and more.
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There are no source code libraries or how-to links for iGoogle Themes. If you know one why not add it?
i'm confius.. but i'll must to learn