There are several layers at which a GNU/Linux system's appearance can be customized. By far the most visible, especially on a multi-user machine, is the login manager screen. KDM (the KDE desktop manager) has a highly-flexible and easy-to-use XML-based theme system. If you can draw what you want, you can make it happen with a KDM theme. I'll talk you through the construction of one simple theme I designed for my ASUS Eee PC.
A few weeks ago, I promised to explain how to create your own custom live CD with Fedora’s new tools. Well, last week Fedora 7 was launched and all the tools you need are available in the repositories. This even includes a brand new graphical tool, put together by the people at Fedora Unity, called Revisor, which will allow you to spin your own live CD or installation material in an unbelievably user friendly manner.