scanner should prompt you to insert the next volume.
I'm not sure how you would go about changing tapes like that on a windows server, since I'm unix.
in unix, if it's a non-jukebox device, merely eject the tape, insert the next one, tell scanner what it wants to know, and proceed.
in unix, if it's a jukebox device, nsrjb -u the device, then nsrjb -ln the next tape (-n for no-mount).
I have a script that handles all that for me, and also disables the device so that other jukebox requests don't try to jack with the drive I'm using for scanning.