I have been in contact with a German Professor at the University of Leipzig and, via the web translation 'bot at Altavista.com, he has informed me that yes indeed, Tetzlaff is a Lusatian name of Slavic origin.If I can read the listing he provided from the book correctly:
"In the book " Lausitzer [Lusatian] surnames of Slavic origin" by Walter Wenzel (Bautzen, 1999) are given by name the following explanations: "
What the above means I have only a small clue - perhaps the numbers above are dates that the names in that form appeared - that or they are some catalog or index number to names, their location or pronunciation...
Any German-speaking people here that can help with this??