I want to install a clustered Exchange 2000 Server machine in my organization, which currently uses Exchange Server 5.5. However, when I attempt the installation, setup fails. The cluster works properly in all respects, but I can't install Exchange 2000 on the clustered server. How can I find out what the problem is?

Although Setup might seem to be acting capriciously, it isn't. You can't set up the configuration you describe because you can't make the first Exchange 2000 server in an existing Exchange 5.5 organization a cluster. The first Exchange 2000 server must run the Site Replication Service (SRS), which synchronizes the routing topology map for the Exchange 2000 and Exchange 5.5 worlds. Unfortunately, the SRS doesn't run on a cluster, which causes your problem. To work around the problem, make your first Exchange 2000 server a nonclustered server; bear in mind, however, that the SRS must then remain operational until you remove the last Exchange 5.5 server in your organization.