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Mikhail Arkhipov on our team recently developed a spell checker add-in to Visual Studio 2005 that allows you to spell check the contents of your ASP.NET or HTML page in HTML view. You need to have Office 2003 installed on your machine in order for this feature to work.
See http://blogs.msdn.com/mikhailarkhipov/archive/2006/04/17/577471.aspx for details including install location.
Try it out today and let us know what you think.