Hi Jim, I have not done this but let me tell you whatever i remember from some article few years ago. Unfortunately, i donot have the article or the link
From Struts 1.1 (i suppose), there is something called DynaValidatorForm is used for server side form validation. There should be a method in this API named validate with action mapping as a parameter.
in Struts1.2 also this is available, it sits below ActionForm in hierarchy and we got to extend this one instead of ActionForm and implement validate method in form and also set the "validate" attribute in action mapping to true and should work as intended.
Moreover, the validations mentioned in validation xml actually generates a javascript method in that particular JSP where the form is used. you can view such automatic js code by view source
May be if you google for dynaValidatorForm you might get more information.