I thought you are referring to the event that after back up session it will eject the tape automatically so you can replace it without pressing the eject button. This option is not supported on NT back up.
I'm using Veritas and that option you're looking is like "Inventory" on Veritas tools. Sorry, I really not sure whether there's an option like that on NT back up, ANYONE?
** There's a lot of limitation of NT back up that's why we buy 3rd party software like Veritas, Arcserve etc. for back up purposes.