The answer to your question is in the READ_ME file. Have a look at the tab "Misc" - specifically the first section that talks about using IH3 with Zen Lightbox.

Quote Originally Posted by DKunev View Post
One question from me about IH3 and Lightbox...


I see that Lightbox changes the file aditional_images.php in which IH3 also has code

When I install Lightbox what should i do with that file? Overwrite? Merge somehow?

Thanks!