Since 4.1 is end of life and no sale, you will not be able to purchase additional software or licensing. If were to create a new cluster, i would create the new cluster as 6.x and move forward.
Since it's a new cluster, you would have to purchase the DLUs and new 6.1 software. For the old cluster, at some point you will have to upgrade it. Which if you have a smartnet contract and are entitled to upgrades, the DLU's and 6.x software is included. (possibly need a new server(s).
What is your current topology? (1) subscriber and Publisher? Or do you have more than (1) sub?
If you had (3) Subscribers and (1) Publisher, you could do this:
Check to make sure the hardware will work with CUCM 6.x
Remove (2) subscribers.
Purchase new DLU's and 6.1 software
Rebuild as Pub and Sub new cluster
Bulk in the phones
Create an Inter cluster trunk
Create a new Unity integration (because you can have multiple integrations with (1) unity server)
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.