Thanks for the follow up to my post. So, if you installed the Office Fluent User Interface XML Schema from:
And you are using VS.NET 2008, then the XSD for the Office 2010 Ribbon should have been installed to:
C:\Program Files (x86)\Microsoft Visual Studio 9.0\xml\Schemas\1033\customUI14.xsd
Are you able to see that file there? If so, you should just be able to specify that file. Otherwise, there may be a problem with your machine if the Office Fluent User Interface code is unable to install.
Anyway, I hope that helps!