Adding users to a group

Sorry to post so soon on same problem, but I haven't solved it yet. I would like to add users to my wiki who are registered as members of xwiki.org. The reason for this is to allow them to log in once, and then be able to edit all the wikis of which they are members, instead of remembering a new login for each wiki. I am entering the users in the Group Object as xwiki:XWiki.loginName where the loginName is the user's login at xwiki.org. I found the FAQ on creating a new group HowDoICreateNewGroups, and followed the instructions. I now have a new group, and have successfully added users to it. Then I go to the Preferences page, and make a new rights rule that gives privileges to the new group. For ex. I select the group, select view/edit and Allow. This doesn't work. The user cannot log into the wiki. I think the problem may be the syntax I am using for the user name. Can someone give me the correct syntax? Is there some other way to do this? Finally, perhaps this isn't possible, and I should just make the users log into more than one wiki? thanks, --elli