Would the Photoshop facility: File > Automate > Contact Sheet II offer the facility you need?
Have you tried the applescript version?
The sample catalog scripts are from 2009, so they might not always work. I wrote my own variation, which lets me spec the page size, the dialog looks like this:
There are JS and As versions you can try here:
The JS version creates Object Styles for the images and labels so you can manipulate the design from the styles after running the script.
Great Applescript, Rob, thanks!
Adobe Bridge's Output module is another way to do it, ton's of customizations options