Maybe Knoppix HD installs should come with a health warning - do not do apt-get upgrade.

This topic has been discussed before many times, but maybe
http://www.knoppix.net/forum/viewtopic.php?t=20369
would help give further insights that might help you decide what to do for the future.
A better way to upgrade Knoppix might be to wait for the next Knoppix CD or DVD version to come out and install that to the hard disk.
Then re-install your personal files from a backup. If the 3.8.1 Knoppix HD install kept you happy for a while then maybe this would be a good bet.
Stable Debian is very stable, but will probably not be the best choice for watching movies, and it comes with OpenOffice 1.1x installed by default.
For word counting type
man wc
at a terminal prompt.
Installing Debian can be hard work, and setting up the upgrade environment is also an art form. To do it anything like properly you need to find out about aptitude, debconf, dpkg, apt-setup, /etc/apt/sources.list, apt-cache, pinning and /etc/apt/preferences, debsums, source versus binary packages and dependencies.
Personally I find Knoppix works well as a HD install. It sets up Linux, Apache 1.3, MySQL and PHP nicely whereas Debian will set up PostgreSQL instead of MySQL by default. This doesn't mean it is impossible to set up MySQL with Debian, but it is harder.

Regards,
Mark