This instructions refer to inserting the popup in a Categories' page layout.
Please, follow the steps to add the popup on your Categories' page layout.
1. In your Categories' page, find Custom Design
2. In the "Custom Layout Update" field, add the following code with your popup id number inside ("1" inside the code should be replaced with your popup id number):
<block type="popupbuilder/PopupWidget" name="popupbuilder"> <action method="_toHtml"><alias>your popup id number</alias></action> </block>
Don't forget to Save the changes! ;-)