Silverlight SDK CHM not working on Vista?
Some people have been having issues viewing content in the Help file (chm) that comes with the Silverlight SDK when using Vista. This is probably due to a security update on your machine interfering with the CHM. To get around this, try right clicking on the CHM, then Properties, and click the "Unblock" button on the General sheet.
http://support.microsoft.com/kb/902225
