Firstly is the Exchange Server Topology Diagramming Tool (ExMap).
"Creating topological maps of your Exchange sites, servers, and the connectors belonging to your organization can be a time consuming process. By using the Exchange Server Topology Diagramming Tool (ExMap), you can automatically generate a Microsoft Visio® diagram of your site topology"
The second is a Exinfo.exe.
Exinfo.exe, which is a information collection and diagnostics tool that provides a range of Exchange 2000 Server system state and Active Directory information. Here is the link: http://support.microsoft.com/default.aspx?scid=kb;en-us;305816#kb1
Note: Both of this tools are for Exchange but they work fine on Exchange 2003.