Make sure your system (Knoppix) is using an Unicode-based locale (UTF-8):
$ locale
LANG=en_US.utf-8
LANGUAGE=
LC_CTYPE="en_US.utf-8"
[skipped irrelevant settings]
LC_ALL=
If the LANG or LC_CTYPE variables do not end in .utf-8 (or .utf8), fix them:
run locale -a and make sure it lists the needed locale (i.e. en_US.utf-8);
if the locale is not listed, uncomment it in /etc/locale.gen:
en_US.UTF-8 UTF-8
and run locale-gen as root;
run export LANG="en_US.utf-8"
run (xterm &) or (gnome-terminal &) to start a new terminal with the new settings applied;
close the old terminal. (It is not enough to change $LANG for the current shell.)
In the new terminal, verify output of locale and check whether it fixes your problem.
Also make sure your filesystem driver is using UTF-8. The NTFS filesystem uses Unicode exclusively, but if you mounted it while having an incorrect locale, the driver might be in a translation mode. Unmount the filesystem and mount it again, while having a correct $LANG. If even that does not help, try adding the utf8 and iocharset=utf8 options to mount...
# mount -t ntfs -o utf8,iocharset=utf8 /dev/foo /mnt
...or switch to the ntfs-3g driver:
# mount -t ntfs-3g /dev/foo /mnt