<<< edit: Optware pckages are most often NOT a single binary. You’re looking for e2fsprogs, which contains all the similar binaries. –brad >>>

But i obtain this:
# mount -o loop bigger.opt.bin optMount
NTFS signature is missing.
Failed to mount ‘/dev/loop4′: Invalid argument
The device ‘/dev/loop4′ doesn’t seem to have a valid NTFS.
Maybe the wrong device is used? Or the whole disk instead of a
partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?

How to mount now !?

<<< edit: Did you check to see if it was mounted? You did not specify filesystem type so it went through all of them until it found the right one. –b-rad >>>

thanks a lot for writing this up! Worked perfectly.

-sasa