"Book fold" is not compatible with printing 2 UP through the printer driver,
as it is already printing two pages per sheet (and it combines pages 40 and
1, 2 and 39, etc., automatically). Text should reflow without any problems;
tables will be more problematic (though setting the table width to 100%
helps). Many users have reported problems duplexing booklets. "Book fold" is
really best used for printing camera-ready copy to be duplexed on a copier
or by a commercial printer. For another method, see
http://word.mvps.org/FAQs/Formatting/BookletPrinting.htm