I have two similar Word mail merge main documents. Each of them uses an Excel
spreadsheet as its data source. When I open one of them, Word opens (as you
would expect). When I open the other one, Word opens _but_ Excel also
launches and the data file is available as an icon on the bottom-screen XP
toolbar. I like that feature, but cannnot figure out how one Word doc "knows"
to launch Excel, but the other does not.

What option/setting in a mail merge main doc would also launch Excel?
(Office 2003)