If installing mutilple java versions, JAVA_HOME is implicit in the windows registry, so the new JAVA_HOME environment variable must preceded system32 in the %path% environment variable.
References
- How to change the default JRE when there are several versions: http://forums.sun.com/thread.jspa?threadID=645735&messageID=3805127
- http://forums.sun.com/thread.jspa?threadID=668703&messageID=3911278
