To perform an unattended install of the Standard ERP client, you need to get the MSI package. Download the installer from Standard Install and run it. When the installation dialog appears, you will find the actual MSI package in the %TEMP% path.
The command line to install the client in C:\Program Files\HansaWorld\Standard ERP\ is (note that "installer.msi" should be replaced with the name of the MSI package you want to install):
msiexec /I installer.msi /quiet /norestart /L*v hwinstall.log TRANSFORMS=:Instance1 MSINEWINSTANCE=1 M4INSTALLDIR="C:\Program Files\HansaWorld\"