my win7 pc has that file, so it is a dll that can be installed into win7. Not a vista only dll or anything
I seem to remember there being a two part process to get the software for my rigol running (1052E)
The ultrascope software and some other NI driver package or something, but they were both on the CD that came with it.
Maybe you should try download a fresh copy of the driver for your scope.
The cd may have been damaged and not installed both parts of the driver properly.