In order to install the Subversion Plugin (subclipse) in Aptana you need to have the Aptana Studio 3 already installed. In the Aptana Studio 3 go to Help -> Install New Software…
Download WordPress package from wordpress.org. Unzip it in C:\Users\…\Aptana Rubles. In Aptana Studio 3 go to Preferences -> Aptana Studio -> Editors -> PHP -> Libraries.