For a poster sized collage, I would not use Pages but Numbers.
Create a new document in Numbers, delete the available table.
You will have a blank area on which you will be able to put many objects (photos in this case).
The doc may be several pages in width and several pages in height.
So, you will be able to print at a normal resolution, not at a reduced one resulting of a zoom process.
Yvan KOENIG (from FRANCE lundi 26 novembre 2007 17:52:49)