What I would do is follow whatever steps retrocity said to get them all together in one file and do some math. Say each image is one inch by one inch, I would increase my canvas size to handle about five across. Then you would have six rows down. Select and link the layers of your first row and use the Align feature in the Option bar and align them by TOP. Do the next set of images for the second row, and so on, and so on...

You can also Distribute across to spread them evenly.
Just merge your layers after you're done.

Yoshi