How do I use only a portion of a document in a mail merge?

[Jennifer C.]

I'm trying to create a mail merge from only a small portion of a large
document. I'm using Office 2003. The issue I'm having is that I can check
boxes to indicate what I want to use, but can't see the line numbers from the
Excel sheet so I know that what I'm checking is correct. Is it possible to
create a mail merge like this with Office 2003? I know that I use to be able
to with previous editions.