Edit: Um, well, perhaps SQL Server 200 is shipping SP4 somewhere, but clearly I meant SQL Server 2000.  I blame the gremlins, I really do!

The download page can be accessed from this link:
http://www.microsoft.com/sql/downloads/2000/sp4.asp

Highlights:

· All updates and fixes released since the original release of SQL Server 2000.

· SP4 provides enhanced performance, serviceability, and security to SQL Server 2000.

· SP4 includes the MS03-031 security bulletin released in July,
2003.

· SP4 improves performance on 64-bit systems with 32 or more processors. (I know I have a couple of these servers laying about my house!)

· SP4 introduces new serviceability functionality that enables you to remove hotfixes applied to SP4 and later versions of SQL Server 2000 running on Microsoft Windows XP and Windows Server 2003. 

!!!!Note: SP4 itself cannot be rolled back.!!!!

· SP4 is the first service pack to service the 64-bit edition of SQL Server 2000.

· Adds the following platform support:

With Microsoft Windows Server 2003 x64 Edition, SP4 provides support for 32-bit SQL Server applications on 64-bit architectures using the Windows on Windows emulator (WOW64). For more information on specific 64-bit platforms supported, see the Windows Server 2003 x64 Editions Product Overview.

Note: SQL Server 32-bit applications, including SQL server client tools, are still not supported on WOW64 for IA64. Also, currently 32-bit Reporting Services is not supported to run on WOW64 on IA64 and x64 platforms running Windows Server 2003 x64 Edition.