The SIOC exporter for Drupal 4.6 is available from:

http://drupal.org/files/projects/sioc-HEAD.tar.gz

Simply install the sioc.module file in your modules directory.

The project page at drupal.org is:

http://drupal.org/project/sioc

Edit: This module has been written for Drupal 4.6.0 and upwards. It will not work correctly in Drupal 4.5 due to some changes in the way forums are linked to taxonomies.