http://msdn.microsoft.com/en-us/library/ms143506%28v=sql.100%29.aspx#DC_Support

Section: Installing SQL Server on a Domain Controller

The biggest issue is reinstalling SQLServer before promo and then after changing from DC to domain meber.

"After SQL Server is installed on a computer, you cannot change the computer from a domain member to a domain controller. You must uninstall SQL Server before you change the host computer to a domain controller."