Windows 2003 Secondary Domain

I have the following situation :

I have a Windows 2003 R2 system and i want it as a secondary domain of a Windows 2003 server.

At the final step of the instalation, show a message that indicate the previus run of the tool adprep.exe and forestrep.exe…

My question is :
Is this necesary with a situation like this ( windows 2003 r2, 2003 ) because i only found information about windows 2003 joning a windows 2000 server…

Thanks for the help .