"The Update Rollup will contain all security-related updates produced for Windows 2000 between SP4 and the time when Microsoft finalizes the contents of the Update Rollup, and a small number of important non-security updates. Because Microsoft believes the Update Rollup will better meet the needs of customers than a new service pack, there will not be a Service Pack 5 (SP5) for Windows 2000. Therefore, SP4 becomes the final service pack for Windows 2000."
Microsoft also has confirmed that there will be no IE patches outside of monthly updates. "The most important thing in security responses is that, if you come out with a fix, it will be a quality fix that won't break applications or introduce more problems."