jQuery Validation: Changing Rules Dynamically

I have a single form that, depending on which radio button is clicked (Login or Signup), displays either:

• email address
• password

or:

• name
• age
• email address
• password

Clicking on the radio button toggles the visibility of the Login/Signup fields:

<form id="myForm">
    <input name="userAction" type="radio" value="login" checked="checked">Login</input>
    <br />
    <input name="userAction" type="radio" value="signup">Sign Up</input>

    <div id="loginFields" style="display:none">
        <!-- Login fields (email address and password) -->
    </div>

    <div id="signupFields" style="display:none">
        <!-- Signup fields (name, age, email address, password) -->
    </div>
</form>

I'm using the jQuery Validation plug-in, and I'd like to use the following rules:

var signupRules = {
    emailAddressTextBox:
    {
        required: true,
        email: true 
    },
    passwordTextBox:
    {
        required: true,
        minlength: 6,
        maxlength: 24,
        passwordValidationRule: true // custom regex added with $.validator.addMethod()
    }
};

var loginRules = {
    nameTextBox:
    {
        required: true,
        maxlength: 50
    },
    loginEmailAddressTextBox:
    {
        required: true,
        email: true 
    },
    loginPasswordTextBox:
    {
        required: true,
        minlength: 6,
        maxlength: 24,
        passwordValidationRule: true // custom regex added with $.validator.addMethod()
    },
    loginPasswordAgainTextBox:
    {
        required: true,
        minlength: 6,
        maxlength: 24,
        equalTo: "#loginPasswordTextBox"
        passwordValidationRule: true // custom regex added with $.validator.addMethod()        
    }
};