Hi,
Something else I just thought about, when I bring in the ESX 4.1 hosts to be in the same vCenter 5.1 with the ESXi 5.1 hosts, can I create a cluster for them and move the VMs from the ESX 4.1 hosts that are not in a cluster into the ESXi 5.1 clustered hosts?
-- Yes, you will be able to migrate ( vmotion ) into ESXi 5.1
** Only if all the CPU lies in same family. If not you have to perform cold migration.
Regards
Mohammed