_book_get_depth() error in export_docbook module

I have successfully installed Drupal 4.7 locally with the intent of using it within my department at work for collaborative authoring of a small book.

Today I began testing the book features, particularly adding some dummy text and attempting to create some output using the export_docbook module.

When I attempt to do so, I receive the following error:

Fatal error: Call to undefined function _book_get_depth() in C:\wamp\www\cms\modules\export_docbook\export_docbook.module on line 58

I have tried applying the patch located in the following issue thread:
http://drupal.org/node/53826

But that has also met with errors. Drupal and all modules were downloaded within the past week.
This has been driving me nuts for much of the day. Please help.