The open source site is at http://sourceforge.net/projects/orm. Open the Code menu to get instructions on how to sync with the SVN, or view the source with the online viewers at http://orm.svn.sourceforge.net/viewvc/orm.
The sf repository is a (manual) mirror of the primary source maintained by ORM Solutions (me). If you are interested in adding code I would strongly recommend you talk to me first. This is a large code base and requires tweaks to things like the DSL-supplied text templates to build from scratch. I don't have copyright permissions to publicly post these modified files.
Note that NORMA setup installs the debugger symbol (pdb) files, which can be used with the source changeset mentioned with each of the releases. You can attach to a Visual Studio instance running NORMA from another VS instance and use the Modules window to associate the symbol files. However, do not F5 the NORMA projects if you have a setup-installed NORMA version on your machine. You will be manually cleaning out your global assembly cache to get things running again. Consider yourself warned. There is more information on how to set up a NORMA development environment in the readme file in the repository root directory.