Paul Andrew announces a new article dropped on MSDN titled 'Understanding Workflow in Windows SharePoint Services and the 2007 Microsoft Office System'. I do find the title a bit misleading because a good chunk of the article is about the OOB approval workflow and for that you must have to install the Microsoft Office SharePoint Server 2007. But, good primer.
The content covers the value of human workflow, a primer on workflow and SharePoint, a description of workflow in Windows SharePoint Services and then for Office SharePoint Server, and finally a comparison describing how to choose between Windows SharePoint Service and Office SharePoint Server.