Even if you are not interested in the software, you might like to see the User Guide, which tries to explain fundamental site index concepts and SDE models as painlessly as possible.
The (free and open source) software, for MS Windows or Linux, can be downloaded from here:
Installer for Windows. Just execute and follow the instructions (thanks to InstallJammer).
Zip file (Windows), for those who prefer a manual installation. Unzip into the root directory and follow instructions in the zip comment or README.txt.
The source code is platform independent.
Spanish translation of User Guide (only from the older version for now) by Christian Salas (U. de la Frontera and U. of Yale). Conference presentation (PDF, 661 Kb).
Here is a list of articles where the method has been used: HTML, BibTeX. Please let me know of any others. Some more theory: doi: 10.1007/s10342-010-0458-0.
Questions, comments, suggestions, are welcome.