Probably the easiest way to achieve an effect like that is to use al_draw_scaled_bitmap(), and scale the bitmap horizontally. (Each page would be an ALLEGRO_BITMAP) It would give you rectangular shaped pages; without perspective. Here's a mock-animation of what it might look like:
Probably the most elaborate way would be to setup a 3D projection and create a mesh of ALLEGRO_VERTEX that deforms like paper as you flip it.
[edit: I don't know why the proportions on that gif are all messed up. hmm. something to do with the forum image embedding?]