var Screen =
{
    getClientWidth: function()
    {
        var availWidth = document.documentElement.clientWidth;
        
        // fixes IE5.x issue    
        if(availWidth == 0)
            availWidth = document.body.clientWidth;
            
        return availWidth;
    },
    getClientHeight: function()
    {
        var availHeight = document.documentElement.clientHeight;
     
        // fixes Opera, Safari & IE5.x height issue
        if(document.body.clientHeight > 0 && (availHeight == 0 || 
            availHeight > document.body.clientHeight))
            availHeight = document.body.clientHeight;	                
        
        return availHeight;
    },    
    getOffsetFrom: function(width, height)
    {
        var availWidth = this.getClientWidth();
        var availHeight = this.getClientHeight();
     
        var offsetLeft = Math.ceil((availWidth - width) / 2);
        var offsetTop = Math.ceil((availHeight - height) / 2);
        
        return { top: offsetTop, left: offsetLeft };
    }  
};