Rails - Aug 2007 - has_and_belongs_to_many polymorphic question

I''ve got a situation where I''m trying to model the following  
relationship:

a ''page'' has multiple lineitems

a ''lineitem'' can be either a ''page'' or a
''entity''

The ''lineitem'' looks like it should be polymorphic but the
''page'' and
''lineitem'' relationship has me confused. It looks like a  
has_and_belongs_to_many but a ''lineitem'' can only exist on one
page
and can refer to any single ''page'' or
''entity''.

If I do has_and_belongs_to_many on both sides isn''t that a two way  
multiple association?

Basically, the model is like a filesystem where a directory can have  
multiple files or other directories, etc. I''m keeping the lineitem  
around because I need a way to order the lineitems on the page.

I''ve looked at the folder example on the wiki but it doesn''t
link
folders back into folders.

Any suggestions?

Thanks.