My PPC G4 machine is running Tiger 10.4.9 and Zimbra v. 4.5.x OS edition for almost a year now. It's directly connected to internet with dedicated IP address. All just works, as on mac ;-)
Question is: HOW to upgrade and move to Intel platform? (I have Intel Mac ready for that). New 5.0 version is compiled only for Intel machines ... but previous version was meant to run only on PPC processors. So it's not possible to "just run upgrade script" - we cannot upgrade on the same PPC machine, and 4.5.x is impossible to run on Intels ... I see catch 22 here.
From this point I see one way - install 5.0 on Intel machine and use imapsync or something like to migrate all accounts to new server.
That's more like "migrating" than "upgrading"... correct your docs accordingly.
Just one more thing - it would be very helpful if we can use specific entry in forum for Mac OS X users only - but it is possible to succesfully run Zimbra on Macs, both servers and clients, just very hard to dig info about our platform dependent questions...