SII is currently being developed under Windows (using Cygwin) and Linux. The first things you need before you can run the program in either OS are:
Currently, Flite must be compiled to run so it would be a good idea to read the README and INSTALL files as suggested on the website.
Windows is not supported at this time.
At this stage, there are only files in the CVS repository. Information on that is located on the Developer's Page