Use a Catalog, or in Word XP and later, it is called a Directory, type
mailmerge main document.  In that document, insert a one row table and into
the cells of that table, insert the merge fields that you want in the
output.  When you execute the merge to a new document, that document will
contain a row of data in a table for each record in the data source.  If you
don't want the cell borders to appear, use Ctrl+Alt+u to remove them.