SystemImager is maintained in SVN at http://svn.systemimager.org . To submit patches for future releases, generate them against the code in SVN. There are typically two active branches at any given time - the current stable branch and the current development branch. If you are fixing a bug that exists in the current stable release, generate a patch against the stable branch. If you are adding a new feature or fixing a bug that is only in the development branch, use the development branch.
Instructions for accessing the SVN repository can be found at http://svn.systemimager.org .