You need to be root to do this.
You can do it graphically by running these commands from a terminal window as user knoppix
su root <enter>
then, at the root prompt
konqueror<enter>
Then you can browse the filesystem and write/copy files to the /var/www directory from within konqueror.

Once you've got plain html pages working you might like to try out the link below and give php, perl and bash cgi scripting a whirl.

http://www.knoppix.net/forum/viewtopic.php?t=21221

Regards,
Mark