Not sure if the core server is fully supported by Altiris. Can you get a list of running services on the server (I don't use Win2008, so I'm not 100% familiar with it). If the service is running, I would think that would be your confirmation that the dagent is running. The next item I would look at if it is running but not reporting in would be to ensure that Win2008 doesn't have any firewall or ipsec blocking it.