QuestionResource Manager in the Notification Server Web admin console shows the "First Discovered" date under the Altiris Agent details section on the
Summaries tab under
Resource Manager >
Resource Summary. Where is this information found in the database?

Answer
The "First Discovered" date that is used by Resource Manager is found in the database's CreatedDate column of the Item table.
A report which can be imported into your Notification Server 6.x console is now attached to this article. The SQL used in the report is as follows:
select T1.createddate AS 'Discovery Date', T1.Name AS 'Computer Name'
from vComputer T0
inner join item t1 on t0.[Guid] = t1.[Guid]
where T0.IsManaged = '1'