Support for Java 8 in Eclipse Kepler 4.3.2 is described here. This basically says specify
http://download.eclipse.org/eclipse/updates/4.3-P-builds/
as the 'Work with' site on Install New Software
and select 'Eclipse Java 8 Support'.
Recent builds of Eclipse 4.4 Luna (since 18 March 2014) have Java 8 support included (but Luna is still under development).
Update: Eclipse Luna (4.4) was released on 25 June 2014