I assume you want to span two pages for each month.
Create the complete calendar in the landscape mode, do all your dates, insert your
images and whatever information you need to add.
Open another instance of Publisher, booklet page setup. You will have to add 24
additional pages for a total of 28...

This is the tricky part.

In the calendar publication, beginning with January, in the file menu, save as,
scroll down in the "files of type", save as a picture , any format will probably
work, although I haven't had too much luck with .wmf (Do not right click and save as
a picture).
In the booklet publication, insert the January image on page 2 and 3, copy and paste
a second January, align so the images are exactly on top of each other and fit the
space. Click on the top image, click the crop tool, crop right to the fold line, crop
the second image left to the fold line. You won't need to do this operation for the
center page (pages 14-15).
This is a roundabout way of doing what you want. Saving 12 images can be tedious.