OmniOutliner 2.2 and later can export documents to Microsoft Word in such a way that the various levels are preserved in Word's Outline view.
Version 1.0.1 is Mac OS X 10.3 compatible.
RequirementsMac OS X 10.2 or later, OmniOutliner 2.2.
*Previously available here
Similar SoftwareOpen Comparison
Suggest Other Similar Software