This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
If you're using Struts version 1.3 or above, the validator-rules.xml file is included in the struts-core-1.3.x.jar file, and should be referenced by the location '/org/apache/struts/validator/validator-rules.xml in your struts-config.xml file.
However, if you're using an earlier version of Struts, you should include the validator-rules file in your WEB-INF directory and reference it as /WEB-INF/validator-rules.xml.