Gallery Preview Rotated

[letsgofishing]

Maybe i'm missing the point - why can't you just draw a rectangle on a page the size you want the overall grid to be. Then set up horizontal guidelines that are say 150px apart. Drag one pic onto the page, position and resize - you can also crop the image using the photo tool.
Drag next image position, resize, rinse and repeat. Once you've completed the grid, select all the images and use Image\Properties\Pop up\Options to create the pop ups. Delete the rectangle guide you used.
Example
http://seascapephotographs.com/sea_and_rocks.htm