[MSWNovice2008]

Hello,
I would appreciate if anyone could show me the right method of using MS word
2007 for the following application.
I am using MS word 2007. I follow Chicago style referencing. When I insert
a citation, in some instances it would cite (Author1 et al 2008) and in other
instance it would cite (Author1, Author 2 and Author3, 2008). Further, in
one instance it even cites (Author1, Author2 et al, 2008).

What I doing wrong? How can I control this?

Thanks,
MSWNovice2008