SQLServer2005SQLAgentUser usergroup is missing in My server Group

We are trying the SQL Replication and the step need us to add account into SQLServer2005SQLAgentUser. However, I cannot find this group in my server although we have SQL Server Agent in our server. I am not sure whether any thing missing when we install SQL Server 2005. How can we add this group back to the server? What is this group doing for?

Thanks