What did you put exactly in lib, jre/lib or jre/lib/ext? Was it the jar mysql-connector-java-5.1.5-bin.jar or something else (like a directory)?
By the way, I wouldn't put it in lib, jre/lib or jre/lib/ext, there are other ways to add a jar to the classpath. You can do that by adding it explicitly the CLASSPATH environment variable. Or you can use the -cp option of java. But this is another story.