How to open specific Edit page in modal popup window

I have following condition for an app trying to develop by PHPR:

1. ord_add.php
   
2. bill_edit.php
   
3. Bill page has setup as child and customer page has setup as master.
   
4. ord_add.php has two fields such as; customerid (dropdown selection field) and Billno (text).
   
5. I put a link "Update Billing info" on the ord_add.php page along with "Billno" field.
   
6. When customer click on "Update Billing Info" link on ord_add.php page then "bill_edit.php?edit1=billid" form should be opened based on "customerid" in a modal popup window.
   
7. I have created the modal popup window as per tips and works fine but it shows whole bill_list.php page instead of what I want in #6 above.
   I don't know how to pass customer id from ord_add.php and billid from bill table to this bill_edit.php page in side the popup window. I have gone through lot of tips in the forum and tried to adopt with no luck. I don't understand where should I tweak the code. I will be grateful if any one please help me with a few code example. Sorry for this inconvenience.