The Gimp (http://gimp.org/ http://gimp.org/) can load _and_ save PSD-files with layers, so you could probably find most of the reverse engineering already done

The Gimp (http://gimp.org/ http://gimp.org/) can load _and_ save PSD-files with layers, so you could probably find most of the reverse engineering already done in the code there. While you are at it, why not just save the file in Gimp format and be done with it? :-)