, What is the difference between the Desktop and the Alternate installation?
The Desktop install CD image contains a graphical installer as well as a live session of Ubuntu, that runs directly off your computer memory and the install media without installing anything to hard-disk. Using the live session installer you have the opportunity to begin using Ubuntu immediately, get an idea of system performance and install if and when ready.
The Alternate CD has an old style, lightweight text-based installer with no Live session available. It also provides you with extra options and configurations not offered by the desktop versions.