Security :: Customizing The CreateUserWizard Control

I am trying to customize the CreateUserWizard control....I added a couple of text boxes with First name, last name in the create userwizard....But the problem is i cannot access the textbox from the code behind....The text boxes which i included in the code are marked in Bold Here is the code for the CreateUserwizard Control

<asp:CreateUserWizard ID="CreateUserWizard1" runat="server" OnCancelButtonClick="CreateUserWizard1_CancelButtonClick"
OnCreatingUser="CreateUserWizard1_CreatingUser" OnActiveStepChanged="CreateUserWizard1_ActiveStepChanged"
CancelDestinationPageUrl="~/Default.aspx" DisplayCancelButton="True" ContinueDestinationPageUrl="~/Default.aspx"
Width="320px" LoginCreatedUser="False" Height="295px" InvalidEmailErrorMessage="Please enter a valid email address.">
<StepNextButtonStyle CssClass="Button" />
<ContinueButtonStyle CssClass="Button" />
<CreateUserButtonStyle CssClass="Button" />
<StartNextButtonStyle CssClass="Button" />
<StepStyle CssClass="WpcClinicalText_Enabled" />
<CancelButtonStyle CssClass="Button" />
<StepPreviousButtonStyle CssClass="Button" />
<WizardSteps>...........................................