See http://www.word.mvps.org/FAQs/Formatting/BookletPrinting.htm .

If you really want to print a booklet, then
http://www.word.mvps.org/FAQs/Formatting/BookletPrinting.htm will help. If
you just want to print two pages side by side, you can use the "2 pages per
sheet" option in the Print dialog. If you want two of the same page, you
need to enter the page number twice. There is another "2 pages per sheet"
option in the Page Setup dialog that allows you to format your document this
way to begin with. Note that both of these options are available only in
Word 2000 and above; the "Book fold" option mentioned in the booklet
printing article was introduced in Word 2002.