To answer my own question:
Yes SQL 2000 can run as a default instance in a Cluster, see BOL below. Only Named Pipes and TCP/IP are available on a clustered instance: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/instsql/in_runsetup_77g3.asp.
BOL states:
How to upgrade from a default instance to a default clustered instance of SQL Server 2000 (Setup)
Note This upgrade is from a default instance (a local installation where the data is on a local disk) to a clustered instance of Microsoft® SQL Server™ 2000. Use this upgrade step if you want to have a default virtual server.
To upgrade from a default instance to a default clustered instance of SQL Server 2000
- On the Welcome screen of the SQL Server Installation Wizard, click Next.
- On the Computer Name screen, click Local Computer. The computer you want to change from a default to a clustered instance should be displayed. You must be on the local computer to upgrade from a default to a clustered instance. Click Next.
- On the Installation Selection screen, click Upgrade, remove, or add components to an existing instance of SQL Server. Click Next.
- On the Existing Installation screen, click Upgrade your existing installation to a clustered installation. Click Next.
- On the Virtual Server Name screen, enter a name for your virtual server. Click Next.
- On the Failover Clustering screen, enter one IP address for each network configured for client access. That is, enter one IP address for each network on which the virtual server will be available to clients on a public (or mixed) network. Select the network for which you want to enter an IP address, and then enter the IP address. Click Add.
The IP address and the subnet are displayed. The subnet is supplied by Microsoft Cluster Service (MSCS). Continue to enter IP addresses for each installed network until you have populated all desired networks with an IP address. Click Next.
- On the Cluster Management screen, review the failover cluster definition provided by SQL Server 2000. By default, all available nodes are selected. Remove any nodes that will not be part of the failover cluster definition for the virtual server you are creating. Click Next.
- On the Remote Information screen, enter login credentials for the remote cluster node. The login credentials must have administrator privileges on the remote node(s) of the cluster. Click Next.
- On the Services Accounts screen, select the service account(s) for the SQL Server services under which you want the failover cluster to run. Click Next.
- On the Setup Complete screen, click Finish. If you need to restart the remote nodes in the failover cluster, you will be instructed to do so in the Setup Complete screen.