I found, quite by accident, that if I add UserID, PortalID, and Authorised to the UserPortals table it effectively allows SSO for the usersID I add.

Does anyone have a scipt for SQL that will do this automatically?  I just need to give access to 700+ user accounts to a newly created child portal. 
Thank you in advance.

"so if you add a user to userportals table it allows the user to log into multiple portals?"

Yes, if I add the associated UserID (inherited from users table) and assign a PortalID (inherited from portals table) then add a "1" to the authorised column the table will auto populate UserPortalID and CreatedDate columns.  I can then logon to multiple child portals with the same ID.  I tested this with 3 separate ID's adding them to 3 child portals
Have a look at Nik Kalyani's blog on the subject.  http://www.devtao.com/2006/08/09/SSO+With+DotNetNuke+4x.aspx

So what your suggesting is a module to do this, and it doesn't sound as simple as executing a script with querry analyzer.  BTW I am using DNN 3.x

Chris Woods has a post here and if I am reading this correctly he explains how to add all users to all child portals.

http://www.dotnetnuke.com/Community/ForumsDotNetNuke/tabid/795/forumid/89/threadid/47304/threadpage/2/scope/posts/Default.aspx

The problem I have is that I don't 100% understand how this is implemented.  If anyone wants to chime in I would appreciate it.  I am looking forward to testing this functionality.