You didn't give any information, but one possibilityis that you downloaded a German iso. For instance, KNOPPIX_V5.0.1CD-2006-06-01-DE - the DE indicates a German iso. -EN would indicate English.

If you got it with a magazine, then the language of the Knoppix should match the magazine. In other words, use an English magazine.

Can you also tell what version you were using.