We will be adding functionality for tight integration with WSS 3.0 in the future. While I am sure you are aware that you can save any file to web folders I assume you are looking for functionality that allows you to save your form to SharePoint, along with meta data something like the functionality provided by Office 2007.

With WWF do you intend to use the workflow services as part of the SharePoint Library or do you want to reference a Workflow directly from the script in the WordFusion form? The first option is easy as it is managed by SharePoint. The second option will be supported by future functionality which will allow you to reference assemblies including workflow components.