If you absolutely want to install it via a script, you would need to ensure the user(s) have the right to install software on the machine.
You could install it via GPO, however, if it is already installed from a different method, you might end up with 2 installs or other problems. MSI packages create their own registration keys in the Registry. Alternatively, you could deploy from the SEPM manager itself.
***************
@Echo off
If EXIST c:\symantec (
IF EXIST c:\symantec\rtvstart.exe GOTO END
)
IF NOT EXIST c:\symantec\rtvstart.exe GOTO MAP
:MAP
net use [drice letter]: \\[server and share of install package MSI] /PERSISTENT:NO
goto INSTALL
:INSTALL
msiexec /quiet /I "[mapped drive from above]\[install package MSI]" INSTALLDIR=c:\symantec
goto END
:END
Exit
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Something like that can work from a batch file or being called from or added to a Logon script. Probably be integrated into Kixstart or Scriptlogic if you use those...