Yes you will need to extend the schema again. 4.0 requires some additional properties.
The only supported security model is the one that we document. 3.X relied heavily on Local System and the Exchange Domain Servers group for Exchange 2000 integrations. Several configurations have problems where Local System is not considered to be a valid security principal and Microsoft continues tinkers with the permissions this group has, often taking away rights that Unity requires. For this reason we required all message store facing services to run with an AD account and explicitly grant right to the account rather than relying on group membership. Our security model for 4.0(3) is pretty solid but yes, you will need two accounts for the services.
If you have Exchange 2003 the Unity partner server must be an Exchange 2003 server and you must have the Exchange 2003 System Manager installed on the Unity server. Once you upgrade to Exchange 2003 you can re-run the Cisco Unity Message Store Configuration Wizard from add/remove programs and upgrade the Exchange System Manager. Its a pretty painless process.
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.