Create popup for button

[miles]

I'm struggling to create a popup window not from a text link but an image button. I want to be able to click on that button and open up a popup window. I have tried this method here but doesn't work for me. Maybe because of 2 reasons.

1- It's a button link not a text link.
2- The button is located in the header tagline which is here includes/languages/english/mytemplate/header.php

Either way, I'm not sure about all that. Just guessing.

The code for my header 'tagline',

// added defines for header alt and text
  define('HEADER_ALT_TEXT', 'Company Logo');
  define('HEADER_SALES_TEXT', '<a href="http://www.mysite.com/gallery.php" target="new"><img alt="button" src="http://www.mysite.com/images/blue_button.jpg"></a>');
  define('HEADER_LOGO_WIDTH', '150px');
  define('HEADER_LOGO_HEIGHT', '100px');
  define('HEADER_LOGO_IMAGE', 'companylogo.gif'); 

So far I tried to change the code to something like this,

define('HEADER_SALES_TEXT', '<a href="javascript:popupWindow('http://www.mysite.com/gallery.php')" target="new"><img alt="button" src="http://www.mysite.com/images/blue_button.jpg"></a>'); 

Tried this also,

define('HEADER_SALES_TEXT', '<a href="javascript:popupWindow(\'http://www.mysite.com/gallery.php\')" target="new"><img alt="button" src="http://www.mysite.com/images/blue_button.jpg"></a>'); 

But still can't seems to work. Can somebody help me on this? Thanks.