OU's in the Active Directory

Check out the OU's in the domain.
http://technet.microsoft.com/en-us/library/bb727085.aspx
http://www.informit.com/articles/article.aspx?p=32080
http://www.microsoft.com/windowsserver2003/technologies/directory/activedirectory/default.mspx
These are three sites that offer more infor on Active Directory and OU's