HTML pop-up window

Hey BHW, im currently using weebly as a host for one of my websites. Now i want to get a window to pop up automatically when somebody views my website. There is a html feature for weebly i can use to do this but im not quite sure if im doing it right since its not working. PLZZZZZZ HELP!!!

the fisrt step it says is to copy this section and insert it inot your </head> section.
<script language="javascript" type="text/javascript">
<!--
/****************************************************
Popup window generator provided for free at Hypergurl
Url: http://www.hypergurl.com
Author: Eric King
Url: http://eak.digitalrice.com
This script is free to use as long
as this info is left in
****************************************************/
var win=null;
function NewWindow(mypage,myname,w,h,scroll,pos){
if(pos=="random"){LeftPosition=(screen.availWidth)?Math.floor(Math.random()*(screen.availWidth-w)):50;TopPosition=(screen.availHeight)?Math.floor(Math.random()*((screen.availHeight-h)-75)):50;}
if(pos=="center"){LeftPosition=(screen.availWidth)?(screen.availWidth-w)/2:50;TopPosition=(screen.availHeight)?(screen.availHeight-h)/2:50;}
if(pos=="default"){LeftPosition=50;TopPosition=50}
else if((pos!="center" && pos!="random" && pos!="default") || pos==null){LeftPosition=0;TopPosition=20}
settings='width='+w+',height='+h+',top='+TopPosition+',left='+LeftPosition+',scrollbars='+scroll+',location=yes,directories=yes,status=yes,menubar=yes,toolbar=no,resizable=no';
win=window.open(mypage,myname,settings);
if(win.focus){win.focus();}}
function CloseNewWin(){if(win!=null && win.open)win.close()}
window.onfocus=CloseNewWin;
// -->
</script>


Then step 2 says to insert this code into the </body> section. Idk where to put this portion at?
Insert the following into the body tag
onLoad="NewWindow('http://adscendmedia.com/click.php?aff=9118&camp=1709&crt=5529&sid=','IPAD','500','600','no','center');"


And if anybody wants to throw at me another idea istead of using this 1...plzzz do so!! Thanks!!