Nice sample application showing how to edit XOML using a rehosted designer.

Then take a look at http://wf.netfx3.com/blogs/wf_team_bloggers/archive/2007/01/23/wfpad-for-windows-workflow-foundation-rtm.aspx or download the code from http://www.schmidt6.com/blogfiles/WF/WFPad.exe .