$.validator.addMethod("regex", function(value, element, regexpr) {          
    return regexpr.test(value);
}, "Please enter a valid pasword.");
 
$("#myBlahForm").validate({
 
    rules: {
        somePassword: {
            required: true ,
            //change regexp to suit your needs
            regex: /^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])\w{6,}$/  
            minlength: 5,
            maxlength: 8,
        }
    }
    ....
);