The latest version of the Server Performance Advisor was released at the end of last week for download here. SPA helps you diagnose the root causes of performance problems in a Windows Server 2003 deployment by collecting performance data and generating comprehensive diagnostic reports that give you the data to easily analyse problems and develop corrective actions.
I'm downloading it now but haven't had a chance to find out more about its capabilities in depth. If it's as good as the first version though, I recommend you giving it a go - especially as it's free. One interesting change, bound to be of interest to many including Eileen and Rod is that SPA 2.0 supports a new management pack which can pass its data through to MOM (Microsoft Operations Manager). Further, it supports on x64 editions of Windows Server 2003.