The BizTalk 2004 Assembly Viewer is a handy tool to visualize deployed BizTalk artifacts. It is not configured by default but it can be configured easily by registering a DLL (see http://msdn.microsoft.com/library/en-us/deploying/htm/ebiz_depl_assemblies_pade.asp?frame=true).
If you open a new explorer window, you will notice a new “BizTalk Server Assemblies” directory. Inside this directory, all deployed BizTalk assemblies are listed and some properties are displayed. If you double click on an assembly, it will open in a new window and you will be able to view its content.