Here's a (somewhat) simplified guide:
1) Put the Ubuntu install CD in the drive and (re)boot your computer.
2) You'll encounter a screen with the Ubuntu logo that asks about the type of installation; type "server" and press ENTER.
3) There will be some screens asking questions; simply follow the directions (or, when in doubt, choose the default option).
4) Ubuntu will install. After it finishes and the computer reboots, login at the prompt with the name and password you provided during installation.
5) The trickiest part: You need to edit a text file, sources.list, in order to install ubuntu-lite-desktop.
After you log in, type the following:
You'll see some text. What you want to do is go down the list, and if you see a line that starts with a # symbol and has the word "deb" immediately after, remove the #. This will allow your computer to access the package servers (known as "repositories") and download/install the files from there.
sudo nano /etc/apt/sources.list
You'll also want to add another line to the end of the file:
This will allow for your computer to download and install the ubuntu-lite-desktop package, which is the point of this exercise.
deb http://blueeyedcreature.net/ubuntu ./
After you add that line, press CTRL-O to save the changes.
6) Only two more commands, and you're ready to go! Type at the prompt:
which will let APT (the utility that communicates with the repositories and handles package downloads/installations) know that you changed sources.list. After that finishes, type:
sudo apt-get update
This downloads and installs the ubuntu-lite-desktop package.
sudo apt-get install ubuntu-lite-desktop
After that finishes, type
to restart your computer. After the reboot, you should be at a new login screen; if you are, then Ubuntu Lite will have properly installed!
As previously stated, if you have any questions, please ask; we're more than happy to help!