What about the following re securing clusters?
From SQL Server 2005 Books Online (search under clusters [SQL Server]\encryption):
Encryption on a Cluster
If you want to use encryption with a failover cluster, you must install the server certificate with the fully qualified DNS name of the virtual server on all nodes in the failover cluster. For example, if you have a two-node cluster, with nodes named test1. property box of SQL Server 2005 Network Configuration to configure your failover cluster for encryption.