workflow revision moderation

I am needing a way to set up a workflow like this:

• Editors add & edit content on the site
• Publishers approve the content
• If an Editor edits content already published, then the current revision stays published online, while the new revision is awaiting approval from the Publisher.

I thought this would be a common workflow that people use, but I can't seem to find a way to do it. I did find the Revision Moderation module (http://drupal.org/project/revision_moderation), but it looks like it doesn't work for Drupal 6.