"Chapters'' that appear before the first chapter of the book are given negative numbers. The macros treat such chapters somewhat differently than ordinary chapters (for example, they are not referred to by number).

Just before the first such chapter, include something like this:

\chapnum=-2

if you have two such chapters, perhaps a preface and a table of contents. In general, set \chapnum to the negative of the number of prefatory chapters you have—for example, if you have only a table of contents, set \chapnum=-1, and if you have preface, brief contents and contents, set \chapnum=-3. Then use the \chapter command just as you would for an ordinary chapter, for example \chapter{Preface}{}.