We have almost the same problem.
Ubuntu is the only Linux distrib supported here due to training issues. Ubuntu Server 6.06 LTS works fine on our test server and is running 5.0.5 FOSS with 9 test users migrated from our legacy mail system.
All has gone well so we have purchased NE and an IBM System x3650 rack server as a production machine to host on.
However Ubuntu Server 6.06 LTS will not install on this machine as it does not recognise the ethernet, raid, and probably more onboard chips.
Ubuntu Server 8.04 LTS works out of the box on this new machine but naturally 5.0.5 NE will not install.
In the entry
Bug 23154 - Ubuntu 8.04 - Hardy Heron Brian Peterson stated that "Please see pm.zimbra.com for platform release schedules. Its should be updated shortly to reflect 8.04 release targets." but there is no section refering to platform support and the only relevant information only refers back to the same bugzilla item.
We are under pressure to inform others of the time plan, but are currently stalled with no information and no way to test the new production machine.
We know 8.04 support is being worked on but is it worth opening a case just to find out the status? We are willing to go with a beta build of 8.04 support for the purpose of hardware testing before setting up the final production system.
Is opening a case worth it?