Cannot Access Global Variable Inside Object Declaration

Well, it turns out IE8 has yet another problem. My code has a global variable (to the object) inside an object declaration that cannot be accessed by a function (that is also global).

The code is like so:
Code:
function myobject(params){
//public
this.initialize = function(){...}
//private
some variables...
//problem variable
var mouse = new Object()
mouse.x = 0;
mouse.y = 0;

//code...
slidecontainer = document.createElement("div");
slidecontainer.onmousemove = function(event) {
if(boo.isIE) {
e = window.event;
mouse.x = e.x + document.body.scrollLeft;
mouse.y = e.y + document.body.scrollTop;
} else {
e = event;
mouse.x = e.clientX + document.body.scrollLeft;
mouse.y = e.clientY + document.body.scrollTop;}}

//this function is in an interval
function moveslides() {
/* this is where I have the problem

It seems that the function doesn't recognize that mouse.x, or mouse for that matter, exists. Mouse is global to the object, so why can't this function access it?
*/if(mouse.x) {
code...
}}}
The page is at [URL] and works on every browser, including finnicky opera, except for ie. The full code is availabe when you right click and view the source on the page.