Do you need all of the Task Management agents?
Here's the script we use:
CTAgentSetup.exe -a /ALL:a /q REBOOT=ReallySuppress
PowerMgmtAgentSetup.exe -a /ALL:a /q REBOOT=ReallySuppress
ScriptTaskAgentSetup.exe -a /ALL:a /q REBOOT=ReallySuppress
ServiceControlTaskAgentSetup.exe -a /ALL:a /q REBOOT=ReallySuppress
PowerSchemeTaskAgentSetup.exe -a /ALL:a /q REBOOT=ReallySuppress
SWDAgentForTS.exe
AeXSWDSolnAgent.exe
Make sure the Altiris Agent doesn't check in and get a GUID while you're building the image.