Upgrading Active Directory - What about CALs?

Hi,

I have an Active Directory Windows Server 2003 with 2 DCs Win 2003, member servers 2003/2008/2008R2, and Windows XP Workstations.

If we upgrade the Active Directory up to Windows Server 2012, installing 2 new DCs wit Win 2012, so we are going to buy 2 license for the server, but, "Do we need to buy CALs for the workstations?".

Txs

Cristian L Ruiz