One of the demonstrations at last nights "Active Directory Diagnosis, Troubleshooting and Recovery" Technet session included the steps to install esentprf.dll to allow monitoring of performance counters for the extensible storage engine (ESE) database underlying Active Directory. The steps to complete this can be found in Chapter 9 of the Windows 2000 Server Active Directory Planning and Deployment Guide - post deployment monitoring of domain controllers. Although this document was written for Windows 2000, the procedure outlined works just as well for Windows Server 2003 as you saw. Here's the link.