To be sure to get intellisense in XML files, you can try the two methods detailed by Jopx here . I say try, cause it didn't work for me. What DID work, was adding a folder with links to the xsd files to the project, as shown by Tony Bierman here
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Read the complete post at http://feeds.feedburner.com/~r/monotonous-moss/~3/221920933/moss-xml-intellisense.html