Subclipse versions are tied to specific versions of the Subversion client API. So you must have a matching version of the Subversion client API (JavaHL) for your version of Subclipse

• Windows Install New Software
• Add
• Name: Subversion
• Eclipse update site URL: http://subclipse.tigris.org/update_1.6.x

Reference: http://subclipse.tigris.org/servlets/ProjectProcess?pageID=p4wYuA