Is there a version of mt for windows, or something similar?

Solution 1:

I do not have a tape drive to test with, but this version of MT for Windows:

http://www.tecno-notas.com/winnt.htm

does claim to support seeking by filemarks.

Solution 2:

http://www.holistech.co.uk/sw/mt/mt.html

MT.exe - command line Windows NT/2000/XP tape utility (GPL)

MT was written to erase an old (tar) backup tape which Windows-XP backup refused to overwrite... but I got curious along the way, and added support for various tape functions:

Erase (Long and short)
Drive and tape status (full details of TAPE_GET_DRIVE_PARAMETERS and TAPE_GET_MEDIA_PARAMETERS structures)
Format (QIC117 only according to the documentation)
Load and unload (eject) a tape
Lock and unlock the tape in the drive
Repartition the tape (if your drive supports it)
Read/dump from tape to a file
Seek by absolute address
Retension the tape
Rewind the tape

so it is a cut down version of the rsm command, but without the complexity (which doesn't seem to be in the published API anyway...)