You have your new x64 hardware, You have fresh copy of Windows 2003 R2 x64, and You want to use it as new, efficient platform for Your DC. Problem? Not really, but I saw question about it few times on Internet and such question was rised by one of Polish Microsoft's customers as well. If few peoles are asking about it – maybe somebody will look for answer on Internet so I've decided to give MSN Search or Google chance to index the answer :).
It's really not a problemu – more like annoyance. Introducing Windows 2003 R2 Dc into domain, requires performing schema extension to be done as I wrote in one of my previous blog entries. Only problem which may occur is that if this is Your first 64-bit DC in forest You may not have machine on which You will be able to execute R2 version of ADPREP.EXE (which on 64-bit medium is also 64-bit). Workaround is so simple, that I'm not really sure if it's worth blog's space :). You have to install Windows 2003 64-bit on Your new hardware from first CD of R2 media, promote it as DC, then transfer (not seize) Schema Master role to this machine and extend the schema (If you are not familiar with such procedure You may be interested in some reading about it). Then you can use 64-bit ADPREP to rise You schema version (version 31 at the end).
Simply, easy … enjoy Your 64-bit Windows 2003 performance and new cool R2 features :).