Since the latest Android SDK releases, Eclipse and its plugins (ADT and CDT) need to be installed manually. To do so execute the following steps:
C:\Android\eclipse on Windows,
~/ Android/Eclipseon Linux, and
~/Library/Android/eclipseon Mac OS X).
Then, run Eclipse. If Eclipse asks for a workspace (which contains Eclipse settings and projects) when starting up, define the directory of your choice or leave the default settings and then click on OK.
When Eclipse has finished loading, close the welcome page. The following window should ...