Putting together 5x5 photos to get 1 photo?

There's also Photomerge from Bridge. Select the 25 images and use this menu item.

I am not completely sure we know exactly what you are wanting to do though.  Are these 25 images that cover a large area that you want to combine into one image?
Was the camera in the same location, and pivoted and tilted to take each frame, or was it perpendicular to each frame, like if you'd scaned each image segment?

Photomerge can handle both situations.

A scripted solution here:

http://andrewnoske.com/wiki/Adobe_Photoshop_-_Scripts_Related_to_Montaging

Are they 25 completely different photos that you want to combine into what some call a 5 x 5 “photo mosaic”? If it’s this, you can do it manually in Photoshop by creating a 5 x 5 guide layout (View > Guides > New Guide Layout), using the Frame tool to drawing 25 frames (one for each grid cell), and dropping one image into each frame. If you happen to be experienced with Adobe InDesign and its Gridify (interactive frame grid creation), multi-file place, and frame fitting techniques, those features could build this in less than one minute because unlike Photoshop, InDesign specializes in page layout.

Or, are they 25 photos of the same scene that you want to assemble into a single 5 x 5 panorama? (Either because the lens wasn’t wide enough, or because you want to use the “Brenizer method.”) This can be done by choosing the Photoshop command File > Automate > Photomerge and loading the images into that. 

Thank you for your swift reply. Sorry, Photoshop is the app I'm working with.

what app?