Eclipse Europa won't work with anything less than JVM 1.5.
But what happens if your client needs a Java 1.4 program? Do you have to download an earlier version of Eclipse?
Actually - no!
You can compile 1.4 programs inside the Europa 1.5 workspace.
Under "Windows - Preferences - Java - Installed JREs", you need to add the path to the 1.4 JVM.
Right click on the 1.4 project.
Under "Properties - Java Build Path - Libraries", ensure that the JRE System Library points to the 1.4 version.
Under "Properties - Java Compiler", click "Enable project specific settings". Set "Compiler compliance level" to 1.4.