This might be too much to ask. Mouse Trail Positioning in Image Handler Java

I am working on a zencart here: http://www.catherineweitzman.com/zen-store/index.php?main_page=index&cPath=71

I have a rollover function that creates, essentially, a mouse trail with static screen xy pixel coordinates that displays an image handler image. My question... is there any way to make the static coordinates (currently 543 an 250 at bottom of code) also incorporate a "margin: auto;" function I would like to apply to the whole site. I am trying to center the zencart pages, but this mouse trail code is stuck in one place and will not center with the rest of the site.

This is probably not the place to ask such an esoteric question, but maybe someone has had a similar experience.
Thanks,
Jesse

// calculate and set position BEFORE switching to visible
var docwidth=document.all? truebody().scrollLeft+truebody().clientWidth : pageXOffset+window.innerWidth-15;
var docheight=document.all? Math.max(truebody().scrollHeight, truebody().clientHeight) : Math.max(document.body.offsetHeight, window.innerHeight);
if(ycoord < 0) { ycoord = ycoord*-1; }
if ((trail.style.left == "-2000px") || (trail.style.left == "")) { trail.style.left=xcoord+"px"; }
if ((trail.style.top == "-2000px") || (trail.style.top == "")) { trail.style.top=ycoord+"px"; }
//trail.style.left=xcoord+"px";
//trail.style.top=ycoord+"px";

trail.style.left=543;
  trail.style.top=250;