To my knowledge Spring Web Flow IDE editor is currently still experimental, and only works against PR3.
After PR3, the Spring IDE team halted development b/c SWF was still evolving rapidly and they felt they couldn't keep up with all the changes.
Now that the API and XML flow definition format have now settled for 1.0 with the latest 1.0 EA release, I would expect editor development to pickup again--as it is clear the editor still needs to be brought in-line with the work that has been done since PR3.
A good question for the Spring IDE team is when do they expect to see a Web Flow 1.0 editor available?
Core Spring Development Team