I\'ve got a C# console app running on Windows Server 2003 whose purpose is to read a table called Notifications and a field called \"NotifyDateTime\" and send an email when
Scheduled tasks can be scheduled to run just once at a specific time (as opposed to hourly, daily, etc.), so one option would be to create the scheduled task when the specific field in your database changes.
You don't mention which database you use, but some databases support the notion of a trigger, e.g. in SQL: http://technet.microsoft.com/en-us/library/ms189799.aspx