Update: Download now available.
Windows Server 2003 Service Pack 1 seems very close with Microsoft expected to announce this pretty much now. Seemingly very similar to Windows XP Service Pack 2, the update will also contain a security update as a main feature.
The WinBeta.org Windows enthusiast site posted a note on Tuesday claiming that Microsoft had released Build 1830 of Windows Server 2003 SP1 to manufacturing. WinBeta also reported that Windows XP Professional x64 also was released to manufacturing at the same time.