[Caspar]

Ok my revised code:

index.htm
//File that loads the script

<SCRIPT LANGUAGE="JavaScript">
today = new Date();
day = today.getDay();

if (day == "2") {
	window.open('newwindow.htm','','scrollbars=yes,resizable=no');
}	
</script>

newwindow.htm
//contents of the popup

<SCRIPT LANGUAGE="JavaScript">
	if (document.all) {
	   w = document.body.clientWidth;
	   h = document.body.clientHeight;
	}
	else if (document.layers) {
	   w = window.innerWidth;
	   h = window.innerHeight;
	}
	var popW = 517, popH = 417;
	var leftPos = (w-popW)/2;
	document.write('<div id="dropin" style="z-index:12;position:absolute;visibility:hidden;left:  '+leftPos+'px;top:100px;width:517px;height:417px;filter:Shadow(color=gray,offX=-5,offY=-5,direction=145)">'); 
	</script>
	<table width="500" border="0" cellpadding="5" cellspacing="1" bgcolor="#41738D">
                <tr> 
                  <td height="160" valign="top" bgcolor="#F0F5F7">
                    <table width="100%" border="0" cellspacing="0" cellpadding="1">
					<tr><td><div align="right"><a href=javascript:void(top.close());><font size="1" face="Verdana, Arial, Helvetica, sans-serif">Close<strong> 
              [ X ] </strong></font></a></div></td></tr></table>
					<table width="100%" border="0" cellspacing="0" cellpadding="5">
                      <tr> 
                        <td valign="top"><p>                                                  
                        <p align="center"><strong><font color="#FF6600">POP UP WINDOW CONTENTS GO IN HERE<br>
                              <br><script language=javascript>document.write(day);</script>

 
                        </font></strong></p>                          </td>
                      </tr>
                    </table>
                  </td>
                </tr>
    </table>
	</div>
</script>