Verification on the form

I have a form with some basic informaiton. I am using the RequiredFieldValidator to validate most of the fields.
But I have two particular textboxes with two checkboxes beside them and I want the user to check at least one checkbox and enter the data in
one textbox, but the user can enter the informaiton to both of the textboxes if they like.
But I have a problem. Even thought the user didn't enter any informaion, the form is processed and submitted to the database. I appreciate it if anyone can help!
Below is the code:
<%@ Page Language="VB" AutoEventWireup="false" %>
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<html>
 
<t ...