Hello,
What version of SEP are you running?
In case of SEP 11.x, check this Article:
How do I create a non .exe OR a .msi Install Package for Installing Symantec Endpoint Protection.
http://www.symantec.com/docs/TECH96388
In case of SEP 12.1, check this Article:
Creating a managed .MSI package in Symantec Endpoint Protection 12.1
http://www.symantec.com/docs/TECH165483
How do I create and configure a custom Symantec Endpoint Protection installation package in version 12.1?
https://www-secure.symantec.com/connect/articles/how-do-i-create-and-configure-custom-symantec-endpoint-protection-installation-package-vers
and
About installing clients with Active Directory Group Policy Object
http://www.symantec.com/docs/HOWTO26773
Creating a GPO software distribution
http://www.symantec.com/docs/HOWTO55429
Hope that helps!!