Win 2008 R2 domain controller in 2003 forest and domain functional level

hi all,

I am thinking on adding a Windows 2008 R2 Domain Controller to my domain. Actually it has a win 2003 SP2 Domain controller and a Windows 2008 SP2 domain controller. The functional level for this domain is 2003 as well as the forest functional level.

Can I do this without having 2003 domain controller being depromoted?

Is it safe though I still have several clients using Windows XP?

Thank you very much for your answers.

Kind regards.