Server Performance Advisor can be found here. It was released a few days ago.
Service Performance Advisor is a server performance diagnostic tool developed to diagnose root causes of performance problems in a Microsoft® Windows Server™ 2003 operating system, particularly performance problems for Internet Information Services (IIS) 6.0 and the Active Directory® directory service. Server Performance Advisor measures the performance and use of resources by your computer to report on the parts that are stressed under workload.Other server roles include system overview (hot files, hot TCP clients, top CPU consumed), print spooler, context switch data and preliminary File Server trace data.
Haven't used it yet, put looking the the details in the overview, it looks like it will be very useful. I'll post an update when I have had a chance to use it in anger.
Orginally found a posting on it on denes 's blog.