I'm running a licensed version of Zimbra 5.05 on Ubuntu 6.06.2 LTS (32bit) and need to upgrade both Zimbra and OS to latest versions.

Which is the advised order if indeed it's possible to do a 'live' upgrade (ie not a 'bare-metal' install of Zimbra with userfile restoration)?

Zimbra 5.05 -> 5.10 and then OS upgrade?
Ubuntu 6.06/32 -> 8.04/32 and then the Zimbra upgrade?

and which Zimbra package would be used to do this?