blue requires a Java 1.5 (also known as 5.0) or greater JVM (Java Virtual Machine). To test to see if you have a JVM installed and what version, at a command prompt type "java -version". If you see something along the lines of "command not found" then you need to install a Java Virtual Machine.

A Java JVM for Linux, Windows, and Solaris can be found at:

http://java.sun.com/j2se/downloads.html

From here, select the version of Java you want to use (must be 1.5 or higher for blue), and then choose the download for your platform. There will be an option to download either the "JRE" or the "SDK". The JRE is just what is required to run java programs and is all that is required to run blue. If you're planning to do java development, then download the SDK as it includes the JRE as well as all of the java development tools.

For Apple Macintosh OSX, a Java 1.5 JVM should be installed with the system. If you don't have it, you can find it at:

http://developer.apple.com/java/