This Plugin needs the jdbc library to work. You can download it here: http://dev.mysql.com/downloads/connector/j/ Store the mysql-connector-java-5.1.15-bin.jar as "lib/mysql.jar" in your craftbukkit folder.

Additional you have to create a "stats.properties" file in your CraftBukkit folder. Here is a Example for the content:

url=jdbc:mysql://localhost/minecraft # jdbc url to the database (currently only mysql >4.1 is supported) user=USERNAME # username for the database password=PASS # password for the database