migration of 2003 server R2 32-bit to 64-bit

I just finished migrating a NT 4PDC to Windows 2003 server 32 bit. everything on the domain seems to be working great. I now would like to know how I can easily migrate a windows 2003 64-bit server into the Active Directory, which will become my main DC.

1) I still have NT 4 BDC machines running necessary software and need to keep in mixed mode, so will migrating to a 64 bit 2003 controller effect that?

2) can I just run adprep /forest and adprep/domainprep, or do I need to transfer FSMO roles?