See the thread "Roman Vassiljev" comment for the installation of Plug - in
https://www-secure.symantec.com/connect/forums/distribute-software-update-plug-altiris-patch-management
"Roman Vassiljev" comment
Usually Software Update Plug-in is rolled out to clients where Symantec Management Agent is installed using policy (Notification Server Console > All settings > Agents/Plug-ins > Software > Patch Management > Software Update Plug-in Install). In this case package with Software Update Plug-in will be distributed to target computers and then installed.
If you want to distribute Software Update Plug-in using another way, you can find installation files at the following location(in case if Patch Management Solution is installed on your NS): "...\Altiris\Patch Management\Packages\Windows Agent\"