Lutz and Subbu,
I don't think it has to be specifically Microsoft Active Directory, but you will need some type of standard Kerberos Key Distribution Center (KDC). Active Directory is the most commonly used one, as the majority of businesses have Windows PCs and thus quite frequently a Windows Domain of some kind. Therefore, the instructions assume AD for the examples they give. However, some other kind of KDC for your network should work as well, but it has to be one that your network clients are setup to trust.
I am in the process right now of setting up SNC without SSO in my environment as well for our SAPGUI clients. We are using AD, however.
Cheers,
Matt