For letters, Word creates a new section for each record in the data source,
which is why you have multiple page 1s. You can either
a/ change the section breaks to page breaks, post-merge (and deal with any
formatting problems that might result) or
b. set up your mail merge as a "Directory" Merge (or Catalog Merge in Word
2000 and earlier). In that case, Word does not insert either a page or
section break after processing each data source record so you need to put
your own page break at the end of the mail merge main document. You may have
difficulty with fields in headers/footers not evaluating in this case.

Peter Jamieson