As you are developing your site, you may want to start at a particular page for testing your web site. By defaults, when you start debugging, Visual Studio runs the page that was currently in focus in your designer. If you set this page, Visual web Developer
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Read the complete post at http://blogs.iis.net/webdevelopertips/archive/2009/06/26/tip-84-did-you-know-how-to-set-a-start-page-for-your-web-site-in-visual-web-developer.aspx