If I may jump in here...
If this is a primarily portrait document with some landscape pages (whether
or not they fall on the back of portrait pages), don't even try to use a
gutter, and for heaven's sake don't try to use Insert | Page Numbers to
insert page numbers. Use the Header and Footer area to set up all headers
and footers (including page numbers), and also note the following:
1. Check the box for "Different odd and even" on the Layout tab of Page
Setup. This will give you a separate Even Page Header/Footer and Odd Page
Header/Footer. Using these, you can put your page numbers on the outside
without using the "Outside" setting in Insert | Page Numbers.
2. This will also permit you to have different top and bottom margins on
landscape pages (an effective gutter). Even though you may not be putting
any text at all in the header or footer on landscape pages (if you're using
portrait page numbers as described at
http://word.mvps.org/FAQs/Formatting/LandscapeSection.htm), you can add
Space After to the header paragraph in the Odd Page Header and Space Before
to the footer paragraph in the Even Page Footer. This will increase the
effective top margin of odd pages and bottom margin of even pages to create
a gutter.
