I having the same problem!
I Install the Internals Viewer for SQL Server 2005 in a machine with Windows Vista 23 Bits. The problem begin because i can see the icon in the SSMS.
After that I Install the 'SQL Server 2005 - InternalsViewer20081228-90.reg'
and after this i try to do a connection with my SSMS and i get the error
The Add-In 'InternalsViewer.SSMSAddIn.Connect' failed to load or caused an exception. Would you like to remove this Add-In? Error Message: The system cannot find the specified file. Error Number: 80070002
But First Congratulations for the product seems so good!