Use either a label or a catalog (in Word XP and later, it's called
directory) type mailmerge main document.  Labels in Word are just tables, so
to use a label type mailmerge, insert a two or three row table in the main
document and set up the necessary information in each cell of the table and
before the first merge field in the second and third (if there is one) row
of the table, insert a <<Next Record>> field.

If you go the catalog or directory route, you only set up the information
once in the mailmerge main document and do not use any <<Next Record>>
fields.  You may have to play around with the paragraph formatting - all
paragraphs, but the last, set to keep with next so that you do not get a
salary slip being split over a page break.