Which IP addresses will I need for 2 instance 2 node cluster. At the moment havean IP address for the each of the machines and another for the cluster. Do we need two more for the sql server instances? I would have thought these would use the cluster IP address (different ports?) but have read a paper suggesting they need to be allocated separately.
You need an IP address for each SQL Server instance, in addition to the cluster's IP address. These are all virtual IPs that shift to the appropriate node of the cluster during failover, and are the addresses their respective names resolve to.