I would suggest using Photoshop. For instructions please post in the
Photoshop forum and you might want to be prepared with some real details
what you are hoping to accomplish.
Creating a collage of photos in ID is really as simple as File > Place... and choosing the photos, then arranging and cropping as you wish. It's not a lot differnt from doing it in Photoshop, except you don't have the Photoshop masking or image editing tools to work with directly. The best place to do the collage will depend on the images and what you want to achieve.