The Mars Simulation Project can be run through Java Webstart by clicking this link.
You can also download the Mars Simulation Project as a stand-alone Java application:
Mars Simulation Project v. 3.01 (includes source code)
ZIP File: MarsProject_3.01.zip
40Mb
Tarball: MarsProject_3.01.tar.gz
40Mb
Updated 9/26/11
Be sure to use the "Recreate Folders" option if it's available when unzipping the download file.
Note: Version 3.01 requires a Java Runtime Environment (JRE) version 6 update 10 or newer. You can download the latest JRE freely from Sun:
http://java.com/en/download/index.jsp