1. Copy the script to your .gimp-2.2/scripts/ directory (or whatever the version you're 
using is)
2. Start The Gimp, or select the Xtns/Script-Fu/Refresh Scripts options (so that it finds 
it)
3. There should now be a menu option Xtns/Script-Fu/Utils/pstolayers.  Click on it.
4. A dialog box should pop up.  Select your file and whichever options you like.  May sure 
the "last page" option does not exceed the number of pages in the document, else you will 
get an error!
5. Click OK and it should load the file page by page (may take a while) and create a new 
image with one layer for each page.
6. You can do various things with the layered image; just clicking "Save As..." and choosing 
gif will let you save as an animated gif; or you can play it back within Gimp, etc.