Microsoft has announced that after 'Longhorn' which has been commercially named as 'Windows Server 2008', there won't be any release of 32-bit operating system.
In 'Server Directions' document, Microsoft quotes :
"However, after the Windows Server Longhorn release, Microsoft will no longer develop server operating system support for the 32‑bit x86 processor architecture. Instead, Microsoft will work with its partners to transition the industry to 64‑bit computing. Microsoft intends Windows Server Longhorn to be the last 32‑bit release of a Windows Server operating system."