Certification testing has been completed for IBM Lotus Domino 8.5 on Windows 2008. Windows 2008, both 32-bit and 64-bit operating systems, is now supported for Domino 8.5.

This applies to both the 32-bit version and 64-bit version of Domino. See the Domino 8.5 detailed system requirements at http://www.ibm.com/support/docview.wss?uid=swg27013072