Firstly, huge thanks for the install guide. Followed it no real problems. Used Ubuntu 6.06 Server CD (i.e not DVD) realease.
Couple of things I found that I thought I'd report back:
1) I didn't have to uncomment anything in /etc/apt/sources.list, was good as it was.
2) Bind didn't install (Don't know why) so I went straight for Bind9 and followed the bind config instructions but put the forwarders in /etc/bind/named.conf.options and zone in /etc/bind/named.conf.local
3) Second lib mod (/opt/zimbra/libexec/zmgengraphs) was line 28 not line 30
Cheers
Bertie
P.s. I have written a Sendmail/Pop3/Imap migration guide to Ubuntu zimbra here
Guide to Migrate from Sendmail/Pop3/IMAP to Ubuntu Zimbra