First of all, omit the -N. It looks like you have set up either nsmb.conf or .nsmbrc in order to avoid authenticating (which makes perfect sense if you use it for scripts).
But the -N option seems to be falsely documented. I have a FreeBSD backup server up and running and it works only without -N.
I am not quite sure your syntax is right beyond that. Either you have forgotten a slash or a backslash plus a mount point.
mount_smbfs -I [ip address/DNS name] //[user]@[machine]/[share] /Volumes/[mount point]
mount -I 10.0.0.14 //backup@freebsd-box/backup /mnt/backup
If you meant
mount_smbfs -I xx.xx.xx.xx -N //dhoffmann@xx.xx.xx.xx/Share\ Volumes/NAS2
then you forgot the mount point. On the other had, if that is what you were trying to do
mount_smbfs -I xx.xx.xx.xx -N //dhoffmann@xx.xx.xx.xx/Share Volumes/NAS2
then you forgot `/' in front of `Volumes' (in Mac OS X of course!).