There are two ways that you can download MazeRunner- either in source or binary form, although Java Webstart is also available.
SourceForge Download - If you choose this, select the most recent release and choose the package to download. If you choose to download the source code, see the Compiling Mazerunner page for details.
You will need to get the source code if you do not have Java 6.0 (1.6). If you want to download Java 6.0 (1.6), see this page for downloads of JRE 6.0 (JDK is availabe from java.sun.com ).
Java Webstart -
If you already have Java 6.0 (1.6), you can just use Java Webstart to automaticly download and run MazeRunner for you. Note to Java 5 users: The current version of Java Webstart does not support the new Java 6, so even though the program will try to start, it will end up crashing in the long run.