No need to use ntbackup. It is easier and faster to simply copy the file with different file name.
ntuser.dat is the user's registry hive. If the user it belongs to was logged on after the last restart, Windows will have a handle on the file and it can't be copied using a script. Otherwise, the code I posted will achieve what you want. Although, after reading jges post, I, too, am unclear of your goal.
-Geates
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-Infected Mushroom
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