Hello,
1. The Secure Login Client sets the SNC_LIB environment variable correctly, it was overwritten by the following SAPGUI installer (with SNC Encryption feature on). New or changed environment variables are only active in new processes, the OS do that handling.
2. You use the Installation Server which comes with the SAP Setup package. For documentation please refer to the SAP Setup Guide, which is part of the Secure Login Client setup package (unzip it). If you already have one for SAP GUI you can integrate the Secure Login Client into a SAP GUI installation.
3. You need a SAP Netweaver Single Sign-On licence for the Secure Login Client.
best regards
Alexander Gimbel