I have passed the last couple of hours trying to downgrade Java to 1.6.0_13 in my attempt to get Google Web Toolkit\'s hosted mode to work on Eclipse.
And it has pro
If you want to downgrade Java you just need to set the JVM that Eclipse uses for compilation:
Window > Preferences > Java > Installed JREs
and then add a new JDK/JRE that you want, in your case Java 5 then check the box next to the JVM/JRE.