NTBackup was removed since Vista. It is possible to install and use NTBACKUP on Vista, but to make it work on Windows 7 takes a bit more work. If you just need to restore files made from NTBACKUP, try using this NTBACKUP restore program that Microsoft
made. I haven't personally tested this but it's the closest thing that could get your backup files.
In a worst case scenario, you would need to use The VirtualPC function to get access to XP's NTBACKUP (hope you have a supprted CPU!).