This is what I use:
:: if the file exists, this batch file has already been executed
IF EXIST "C:\Program files\altiris\ns7.txt" GOTO END
:: If we keep going, we know the PC doesn't have the NS7 agent installed yet so we can run clean ups first
"C:\program files\altiris\altiris agent\aexagentutil.exe" /clean
"C:\program files\altiris\aclient\aclient.exe" -silent -remove
:: post clean up now install agent
\\location of this file\aexnsc.exe /install /s /ns=nsservernamehere
:: creates the marker file for future runs as ns7 agent has been run
CD "c:\program files\altiris"
ECHO y > ns7.txt
GOTO END
:END
:: exits batch file
EXIT
simple .bat file that is called via a GPO startup script.
(Yes it could be much cleaner, but I'm not too worried at this point as its not being deployed company wide yet)