The only way I have figured out to set the Estimated Hours was with database access and a SQL query:
UPDATE t
   SET StTaskEstimatedHours = 4
FROM dbo.syn_Task t
WHERE t.EndModifiedTime = 0 AND t.DeletedTime = 0
  AND t.StTaskNumber = {task.Number}
                  jasonpenny
                   2010-07-16 12:51:55