First step would be to check the agent.
In the 'McAfee Agent Activity Log' does your ePO server name appear at the top? http://<computername>:8081
or in the agent log C:\Documents and Settings\All Users\McAfee\Common Framework\DB\Agent_XXXX.xml are there any lines like
<Log component="4" time="2013-07-17T14:01:12" type="3">Checking update packages from repository ePO_<YOUREPOSERVER>.</Log>
If you can work out how the agent is controlling the update process then you'll have a better idea where the computer might be. If it's definitly not in ePO the the computer might be pulling DATs via a UNC repo that has been manually configured. If line above is in the agent logs then it's doing an ASIC and will definitly be in ePO just hidden away in the lost and found folder may be.
Just another question are your XP deployements cloned/imaged? and if yes did you install the agent into the 'golden' image before deploying?