As far as I know there is no way to determine the sequence of fields in the
Edit Recipients dialog box, unless you are willing to name your fields in
such a way the Word gets it right. As far as I know, the underlying
assumption of Word Mailmerge is that you are merging address info. of some
kind, and once it finds fields with the types of names you find in addresses
(Firstname etc.) it imposes its own sequence in the Edit recipients box.

For some types of data source you can get the old "data form" style of
editing by using Tools|Customize to select the Mail Merge Data  Frm or Mail
Merge Edit Data Source command from the All Commands category and drag it to
a toolbar.

Peter Jamieson