So, I "searched for new software" under the help-tag, downloaded the files from the provided link, let Eclipse do the rest until i could click "finish" and finally restarted Eclipse.
During the installation-progress, Eclipse asked me if I trusted a certain certificate that was downloaded. I guess that is normal.
After the restart of Eclipse, I couldn't find an "Android"-Tag in Window/Preferences. It was simply not there! I uninstalled Eclipse once and reinstalled it, made all the steps again and finally restarted Eclipse again, but it was still not there! I couldn't add the ADT-Plugin to Eclipse.
I'm using the most recent Eclipse.
(I do already see the DDMS perspective and can activate it somehow :O)