There is a new security feature in 9.0 that by default prevents HTML and scripting in text block controls. You can override this functionality in the Security Workbench Text Block Control security by setting the Application Encoding option to No.
As David mentions, you can then open and close your window using the window.open() and window.close() JavaScript methods, eg:
<font class="small">Code:</font><hr /><pre><script type="text/javascript">
mywindow = window.open("http://www.google.com", "mywindow", "location=1,status=1,scrollbars=1, width=100,height=100");
mywindow.close();
</script></pre><hr />
Embed some code along these lines into the text block control using the Add Segment system function.
The method that we generally use is to create JavaScript functions (eg: openURLwindow, closeURLwindow) to perform the open and close and add these to a text block control at the top of the form. Do this in Post Dialog is Initialized. And then when you want to execute one of these functions add the following to another text block control:
<font class="small">Code:</font><hr /><pre><img src="/jde/share/images/spacer.gif" onload="openURLwindow('www.google.com')"> </pre><hr />