a server OS was never required but always recommended for production use. IIRC SEC4.0 could only forcibly be installed on Win7 - but only because Win7 still new at this time, not because it wasn't a server OS. I've run all 4.x and 5.0 successfully on Win7. Please see here: http://www.sophos.com/support/knowledgebase/article/113278.html
a server OS was never required but always recommended for production use. IIRC SEC4.0 could only forcibly be installed on Win7 - but only because Win7 still new at this time, not because it wasn't a server OS. I've run all 4.x and 5.0 successfully on Win7. Please see here: http://www.sophos.com/support/knowledgebase/article/113278.html