The plan is to switch to new hardware for our BM server, then upgrade the
old one from NW 5.1 to NW 6.5 and have it cluster with the new one.

What would be the recommended order of things here? I have just installed
the second NIC in the new server; it's already configured with one NIC as
PRIVATE. Do I, e.g., want to configure the new hardware with the same IP
address as the old one, first taking the old one out of service?

Thanks in advance.