A little further follow-up. I think from reading your other thread, Joe, that your Linux installation itself is either broken or corrupted. Too much that's going on in that thread looks suspiciously like packages that should be part of your operating system aren't there. Part of what concerns me is, though I'm no Linux guru, I have never seen a Linux installation that didn't include crontab in the base install. Makes me wonder if your install image is broken.
Questions:
1) What image did you use to install your Ubuntu server? The image I used was ubuntu-6.06.1-server-i386.iso from the server 6.06 LTS portion of the download page at ubuntu.com.
2) Did you get all the packages Zimbra required (including perl, which it doesn't ask for) installed before you ran the Zimbra install?
3) After you verified that DNS was working and you installed your dependencies, did you run apt-get update and apt-get upgrade to patch your install to current versions of installed modules?
All of these things need to be done before anything from Zimbra even touches the system. My own limited, but painful experience tells me that you can't install packages after the fact and have Zimbra work correctly.
And if I'm stating the obvious to someone who already knows, please accept my humble apologies. . .
Dan