Organization Unit for Service Accounts

I am trying to install sharepoint portal server. I am trying to use Service accounts for the purpose of sharepoint administration related tasks. I have to answer as to where to create these service accounts.

What is the Active Directory Structure for the OUs created for these accounts? How come no one gives a clear answer on what organizational unit these accounts fall under? (Sharepoint_OU? SQLServer_OU?) Again, where are these OUs created? Are they top-level OUs? Or they created under the ITDepartment_OU? Please help. I am going crazy trying to figure out where to create these OUs & User Accounts under them.