I had the same thing but I had only disabled network discovery against our known server VLANs. I forgot about the collection of "Discovered Computers with No Altiris Agent Installed" as well as the policy that deploying the agents against that collection.
I also wound up with about 25 servers that were so destroyed by trying to install the NS6 agents on top of the NS7 agents that I wound up having to "aexagentutil.exe /clean" them and then redeploy the NS7 agents.