It's a pain... which version of publisher?
centre fold?
the 2007 version is much better - there is a wizard the hardest part is working out which way up to put it back in
(do help on double sided printing - no duplex for an easy to follow step by step)
for 2003
with just 4 sides it's a doddle just print page 1
(take the "print as booklet" option - which prints 1+4 reinsert
then do it again with page 2 (+3).
with 12 pages ... the easiest way is to use a photocopier
the other way is to split the booklet into 3 seperate pamphlets
pages 1, 2, 11, 12
3,4, 9, 10
5, 6, 7, 8
phew!