Were you ever able to get a test environment up and running with multiple versions? I have a SQL Server 2008 R2 2-node cluster built and running with 3 instances. I need to migrate a 2005 instance to this 2008R2 cluster and I am wondering if installing 2005 into a cluster that is already running 3 instances of 2008R2 is going to be an issue. Let me know?