You don't need to make the folders visible to do this, but you do need to make the changes using an account with Administrator privileges. You should be able to navigate to the required folder simply by pasting:
C:\Documents and Settings\All Users\Application Data\Microsoft\Office\Data\
into the Windows Explorer/File Manager Address bar. You should also ensure no Office applications are running when you edit the file permissions for, or delete, the Data.dat file.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]