Recently I have to run PSSDiag in a BizTalk 2004 customer installation. PSSDIAG is a Tool used by support and escalation engineers at Microsoft and it is used to collect a huge amount of information in order to troubleshoot problems in BizTalk deployments. (There are PSSDIAG tools for different technologies)
When running this tool it is needed to choose the host instance target for the information collected but the interface have only GUIDs in the combo box as showed in the figure:
In order to know what GUID belong to a corresponding host you need to go to services.msc console and look for BizTalk services (HOSTS) then open the properties windows and see the Service name.
After that you may choose the appropriate host/GUID in PSSDiag Tool.