There are several ways to do this but the easiest is to take a look at your
printer driver options because booklet printing is often an option.
There are macros available to automate this for you too. See
http://word.mvps.org/faqs/macrosvba/BookletMacro.htm.
You can also print your document as a PDF and there are sites you can upload
it to on the Internet that will reformat it into a booklet. I also believe
that Adobe Acrobat Versions 7 and 8 can readily convert a document into a
PDF booklet.
I suggest that you search Google with 'Print Booklet from Microsoft Word'
and check out the many options.