I've attached two scripts that could be useful for you.
BoxesFromTextures.ms: collects all textures and opacity maps from a folder, and creates boxes in the scene with Standard Materials using these maps. It uses the Forest maps scheme (<map>.jpg for texture, <map>_o.gif for opacity), but you can modify it.
Once you have a box with each material, use in Forest "Add Multiple Custom Objects" button to add them to the Geometry List. Now, you can use the second script:
SetForestProperties.ms: modifies properties of the selected Forest object. This sample sets geometry to "Template", width to 10, height to 20.
You must modify the scripts to use your own textures and Forest properties, but using them you can automatize the creation process.