Question : Upgrade Path Win 2003 Std. (32-bit) Environ. to Upgrade to Win 2008 R2 64-Bit

The present environment consists of all (20 or so) 32-bit Windows 2003 R2 Standard SP2 servers (including 2 DCs on the same OS).

I would like to upgrade the domain/domain controllers to Windows 2008 R2 64-bit and wanted to know what the best way to approach this would be. Should I simply build out a new host with Win 2008 R2 64-bit and DCPROMO it to take on all the roles? Any specific build or will regular Standard work fine.

Answer : Upgrade Path Win 2003 Std. (32-bit) Environ. to Upgrade to Win 2008 R2 64-Bit

Cross architecture upgrades are not supported (x86 to x64).  Your only choice would be to bring up new servers and decom the old servers after transferring the roles.