As new version of Windows 2003 was shipped new question started to pop-up on newsgroups – how to deal with schema incompatibility between Windows 2003 and Windows 2003 R2 when new DC is added? I've decided to highlight this here because more and more such questions can be seen on the Internet.
Windows 2003 R2 brings some new schema extensions and Windows 2000 or Windows 2003 has to be prepared to incorporate R2 DC as it was previously with WIndows 2003 in Windows 2000 domain. To do this new version of ADPREP.EXE has to be used. This new version is located on the second CD from Windows 2003 R2 media. If You want to add Windows 2003 R2 DC to Your network You have to run ADPREP /FORESTPREP command from drive letter\CMPNENTS\R2\ADPREP directory.
Schema extension procedure for this updates is exactly the same as for any other updates. If you are interested in some comments about this process, You can check my blog entry on this topic.
Here is bit of Technet documentation regarding extending the schema for R2.