If your desktop is hidden by all the windows you have opened, KDE offers you two solutions when you middle-click on a blank space in the desktop to open the right-click menu. Selecting Unclutter Windows disperses open windows equidistant around the desktop. Should that not be enough, select Cascade Windows to arrange in a neat stack that starts in the upper left corner of the desktop, with every subsequent window indented more from the top and left sides.
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Although technically a separate project from KDE, KOffice is so closely associated with the desktop from which its name derives that it should be mentioned here. Besides the usual trio of a word processor, slide show program and spreadsheet, KOffice includes eight other programs, including a data base, rasterized and vector graphic editors, and a project manager. If you are an advanced user of such programs, you may find that KOffice programs too basic for your needs, but, for beginning or intermediate users, they are probably more than enough.
KDE is currently undergoing a massive rewrite, due to be released in mid-January 2008 as KDE4. When that happens, you can expect even more configuration options and special features, as well as several changes. For example, from the KDE4 beta, it looks as though Konqueror is going to cede its role as file manager to the more capable Dolphin. Similarly, the font installer is supposed to receive the enhancement of being able to activate and deactivate groups of fonts.
Until then, these tips should be more than enough to keep you going. Learn the details of current KDE now, and you'll be ready to take advantage of the new features coming in January.