Netscape 6 Load A Page Problem

I am using a little work around to get the "inner width" before the actual page loads. This is done by a PHP file wich sets a session variable. It's no problem, if you don't "speak" PHP in this case.

I call a js file which finds out the inner width. This js than loads a php file which does the job.

Everything works fine in IE5+ but unfortunately not in NS6. NS4 doesn't need to be supported. Here is the code to call the file including teh width variable.

document.open();
document.write("<script language="JavaScript" type="text/javascript" src="/includes/save_width.php?width="+w+""></script>");
document.close();

Any idea, why this doesn't work?