Getting PythonCard from CVS
The latest release of PythonCard is available at http://sourceforge.net/project/showfiles.php?group_id=19015
If you would like to keep up with changes and bug fixes to PythonCard between releases you'll need to checkout the PythonCardPrototype package from cvs.
cvs is the Concurrent Versions System which is the most popular open source, source code revision control system and what SourceForge (SF) uses to manage source code for all the projects hosted on SF. The documentation page for cvs is at http://www.cvshome.org/docs/
The main cvs page for the PythonCard project is at: http://sourceforge.net/cvs/?group_id=19015
I went ahead and tracked down some of the previous relevant posts in the archive:
My instructions for using the command-line cvs tool in Windows: http://aspn.activestate.com/ASPN/Mail/Message/PythonCard/1048235
David Primmer's reply suggesting the GUI Windows cvs client, TortoiseCVS http://aspn.activestate.com/ASPN/Mail/Message/PythonCard/1052572
Personally I don't like the icon changes TortoiseCVS does to files to indicate they are checked out and since I typically have a command prompt open on my machine anyway, it doesn't make using cvs any simpler for my needs, but it does work.
Sections 6 and 7 of the SourceForge documentation page http://sourceforge.net/docman/?group_id=1 have additional cvs info and instructions for Mac classic, Mac OS X, Unix/Linux, etc.