Question : Raise domain and domain forest level

I have network with Windows Server 2008 R2 and Windows 2000, Win XP, Win 7 computers. Server runs also Exchange 2010.
I want to raise domain level and domain forest level from Windows Server 2003 to Windows Server 2008 R2.
I read that this change does not have effect to computers, but only to domain controllers inside Active Directory. I cannot use older DC than Server 2008 R2. I will be able to use Windows 2000 PCs and newer.

Am I correct?

Answer : Raise domain and domain forest level

Make sure that you are not going to use any 2k & 2k3 servers in future, If not..surely you can perform this task.