Tonight we posted SP1 for Windows Server 2003. You can find links to the various downloads on the Security Developer Center. This page has links to the 32-bit builds and to the Itanium builds. (If you don't know what a checked build is don't use that one. A checked build has debugging information in it an it's usually slower than a release build.)
Windows Server 2003 SP1
Windows Server 2003 Service Pack 1 (SP1) includes the latest updates, enhancements, and new functionality for Windows Server 2003. SP1 can help to improve the security, reliability, and performance of Windows Server 2003.
Also be sure to check out the TechCenter page for the SP here.