Please note, this example uses the 'target' attribute, which will render your code non-compliant with the XHTML 1.0 Strict standard.

Method 1 -New Page Loaded- Popup

The methods on this page have been tested on Windows XP, using Internet Explorer 6.0, Firefox 1.5, and Netscape 7.2.
This is the popup window (named myWindow) opened directly from a hyperlink using a named target.

Javascript can be used to change the URL in the initial window (the one that opened this popup window).
To implement, put this HTML code in your popup window:
<a href="#" onclick="javascript: window.opener.location='page2.asp'; window.opener.focus();">Change URL in starting window</a>
Change URL in starting window