Yes, yes I know… the next version of Unbuntu is due any day now but this is a great tute from HowtoForge – Linux Howtos and Tutorials
This is a detailed description about the steps to be taken to setup a Ubuntu based server (Ubuntu 5.0.4 – The Hoary Hedgehog) that offers all services needed by ISPs and hosters (web server (SSL-capable), mail server (with SMTP-AUTH and TLS!), DNS server, FTP server, MySQL server, POP3/POP3s/IMAP/IMAPs, Quota, Firewall, etc.).
The site also carries “Perfect Setups” for a number of other distributions.