When you are trying to install Android Development Tools (ADT) plugin for eclipse you might face with an error like "Cannot complete the install because of a conflicting dependency".
You can rectify this issue first by trying to run Check for updates in eclipse (above image). Most probably you will get a list of components needing update. Try to update each listed module one by one. After each successful update try to install ADT plugin again until you can successfully install it. For example, after successful update of "Eclipse IDE for Java Developers" I was able to install ADT plugin. The update process fixes the conflict dependency.