The gadget loads by default Google Calendar's homepage, but you can change the URL from the settings: click on the small arrow from the gadget's title bar and select "Edit settings".
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Another useful gadget has a rich text editor and you can use it to create content or to paste code from other pages (like Yahoo Video's embeddable code).
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iGoogle should have more bare bones containers that can be filled with user's content: HTML code, web pages, dynamic images or structured data and add them to the gadget creator page.