I agree with Jessica and PS3kid, Ubuntu is just a Linux Flavour and you need to master different demons.
(demon definition > http://linux.about.com/cs/linux101/g/demon.htm)
my advice
1.- Install Ubuntu
2.- buy some O'Reilly books on Linux Server Administration
like this one> http://oreilly.com/catalog/9780596102487/
3.- read the online how-tos
http://www.linux.com/ldp-index
read and learn:
- basic shell commands: ls, cd, mkdir, rmdir, cp, ps, chmod, mount, etc
- basic shell scripting
- linux file structure
- How to create user accounts
- How to configure samba
- How to configure DHCP
- How to configure DNS
- How to configure firewall (iptables)
- How to configure squid (this is a proxy server)
- How to configure sendmail (if they have an email server)
- How to configure apache (if they have a web server)
there is a graphical tool for doing this tasks but as you master linux you will find out by yourself
good luck