passing select option to popup dialog

Dear all,

I have the form with select option control. It will process the delete user function. I want to show the popup dialog with showing some user information and confirm delete button. How to pass information from form to popup dialog?? As I try to do below but seems something wrong.
<select id="sellerID"..> </select> // it will assign hidden variable userID after onchange on select.
<input type="hidden" id="userID" >
<a href="#popupdialoig" var1=<?php echo $username;?> ...> click </a>