Here's an alternative way to do the final assembly step in case you don't have Photoshop, it has less options and control over the final result but still leaves you with something you can use.Download and install Google's Picasa2
(Installer, 5MB EXE)
Import your scaled images folder into Picasa2.
- Picasa Help
With the folder selected in the left pane, click the menu Create->Picture Collage, choose Picture Grid, click Create, wait a bit and you're done.
You end up with a square image that you can open up in Photoshop and crop/resize if need be.