How to join an Active Directory domain in Lion? where do I begin in joining an OS X Lion workstation to an existing AD Domain (Server 2008 R2)?
Looks to me like it's under System Preferences > Users &amp; Groups > Click on 'Login Options' > then click 'Join' button next to where it says "Network Account Server".

Then the dialog box that comes down allows you to enter the AD domain server there. Click Ok.