We just got asked to install some software on the workstation via the Login Script ... and you know the challenges faced there (credentials and security).
I think I already did what you are looking for.
I made a script that checks in the uninstall strings of the registry, by "DisplayVersion" , if some software is installed. If it is not, it starts the installation. You should just be able to create a "silent" installation. Like Les said, only the Computer Accounts that need the software (Domain Computers?) need Read access to the software.
Group Policy Computer Startup Software Installation Script
