LANDesk uses commands in the unattend.xml to install the agent. It sounds like you made one unattend and are also using the LANDesk one Windows should normally aggregate any unattend files it finds and process them. Is the LANDesk unattend getting to the machine?
Once it is done, you can go to C:\Windows\Panther and you will find an unattend.xml in there. That one should be changed a bit, with parts added saying a particular pass was processed and sensitive data removed. You can use that to see if the commands were processed, or maybe Windows didn't find the unattend.xml that has the agent install commands in it.
There are also some sysprep logs in there that may help out.