I only resorted to installing the extensions on the administrator user after failing to get the preview to work in my normal working user profile. No matter what combination of normal dreamweaver start, start as administrator, or compatibility settings I use, I can't get the preview to work in my normal working user profile.
But as soon as I enabled to administrator account and tried installing there, everything worked easily.
So obviously there is a Win7 permissions problem in there somewhere, but I have no clue how to solve it other than just having to do my design work in the administrator user, which I would prefer not to do.