hjælp til Drop in banner position

Hejsa...

Jeg har fundet et drop in banner på dynamicdrive.com, og det er i sig selv fint nok.
Der er dog et enkelt problem (ja det største er at jeg ikke kan finde rundt i Javascripct).
Man kan underligt nok kun definere positionen i pixels... Det må da give problemer hvis man ex. satte boxen til at være 500 px fra venstre. Så ville den passe fint i midten til folk med 1024x768 i skærmopløsning, men ikke til 800x600.
Kan man lave det om, så man kan definere 50% i stedet!?

Koden ser således ud:

/* Placeret i Header */

<style type="text/css">

#dropinboxv2cover{
width: 320px; /*change width to desired */
height: 220px;  /*change height to desired. REMOVE if you wish box to be content's natural height */
position:absolute; /*Don't change below 4 rules*/
z-index: 100;
overflow:hidden;
visibility: hidden;
}

#dropinboxv2{
width: 300px; /*change width to above width-20. */
height: 200px; /*change height to above height-20. REMOVE if you wish box to be content's natural height*/
border: 2px solid black; /*Customize box appearance*/
background-color: lightyellow;
padding: 4px;
position:absolute; /*Don't change below 3 rules */
left: 0;
top: 0;
}

</style>

<script type="text/javascript">

/***********************************************
* Amazon style Drop-in content box- © Dynamic Drive DHTML code library (www.dynamicdrive.com)
* Visit DynamicDrive.com for hundreds of DHTML scripts
* This notice must stay intact for legal use
* Go to http://www.dynamicdrive.com/ for full source code
***********************************************/

var dropboxleft=500 //set left position of box (in px)
var dropboxtop=250 //set top position of box (in px)
var dropspeed=15 //set speed of drop animation (larger=faster)

//Specify display mode. 3 possible values are:
//1) "always"- This makes the fade-in box load each time the page is displayed
//2) "oncepersession"- This uses cookies to display the fade-in box only once per browser session
//3) integer (ie: 5)- Finally, you can specify an integer to display the box randomly via a frequency of 1/integer...
// For example, 2 would display the box about (1/2) 50% of the time the page loads.

var displaymode="always"

///Don't edit beyond here///////////

if (parseInt(displaymode)!=NaN)
var random_num=Math.floor(Math.random()*displaymode)
var ie=document.all
var dom=document.getElementById

function initboxv2(){
if (!dom&&!ie)
return
crossboxcover=(dom)?document.getElementById("dropinboxv2cover") : document.all.dropinboxv2cover
crossbox=(dom)?document.getElementById("dropinboxv2"): document.all.dropinboxv2
scroll_top=(ie)? truebody().scrollTop : window.pageYOffset
crossbox.height=crossbox.offsetHeight
crossboxcover.style.height=parseInt(crossbox.height)+"px"
crossbox.style.top=crossbox.height*(-1)+"px"
crossboxcover.style.left=dropboxleft+"px"
crossboxcover.style.top=dropboxtop+"px"
crossboxcover.style.visibility=(dom||ie)? "visible" : "show"
dropstart=setInterval("dropinv2()",50)
}

function dropinv2(){
scroll_top=(ie)? truebody().scrollTop : window.pageYOffset
if (parseInt(crossbox.style.top)<0){
crossboxcover.style.top=scroll_top+dropboxtop+"px"
crossbox.style.top=parseInt(crossbox.style.top)+dropspeed+"px"
}
else{
clearInterval(dropstart)
crossbox.style.top=0
}
}

function dismissboxv2(){
if (window.dropstart) clearInterval(dropstart)
crossboxcover.style.visibility="hidden"
}

function truebody(){
return (document.compatMode && document.compatMode!="BackCompat")? document.documentElement : document.body
}

function get_cookie(Name) {
var search = Name + "="
var returnvalue = ""
if (document.cookie.length > 0) {
offset = document.cookie.indexOf(search)
if (offset != -1) {
offset += search.length
end = document.cookie.indexOf(";", offset)
if (end == -1)
end = document.cookie.length;
returnvalue=unescape(document.cookie.substring(offset, end))
}
}
return returnvalue;
}

if (displaymode=="oncepersession" && get_cookie("droppedinv2")=="" || displaymode=="always" || parseInt(displaymode)!=NaN && random_num==0){
if (window.addEventListener)
window.addEventListener("load", initboxv2, false)
else if (window.attachEvent)
window.attachEvent("onload", initboxv2)
else if (document.getElementById || document.all)
window.onload=initboxv2
if (displaymode=="oncepersession")
document.cookie="droppedinv2=yes"
}

</script>



/* Placeret i bunden ved </body> tag */


<div id="dropinboxv2cover">
<div id="dropinboxv2">

INSERT YOUR CONTENT HERE. DO NOT REMOVE THE TWO OUTER DIVS<br>
<p align="right"><a href="#" onClick="dismissboxv2();return false">Close It</a></p>

</div>
</div>


Håber nogen kan se hoved fra hale... :)