function openCentered( url, target, options, popupWidth, popupHeight )
{	// set the defaults
    var availableWidth = 800;
	var availableHeight = 600;
	var leftFirstPixel = 0;
	var topFirstPixel = 0;

	if( screen.availWidth )
	{
		availableWidth = screen.availWidth;
		availableHeight = screen.availHeight;
	}
	else if( screen.height )
	{
		availableWidth = screen.width;
		availableHeight = screen.height;
	}

	if( screen.availLeft )
	{
		leftFirstPixel = screen.availLeft;
		topFirstPixel = screen.availTop;
	}

	var leftPos =  leftFirstPixel + (availableWidth-popupWidth)/2;
	var topPos = topFirstPixel + (availableHeight-popupHeight)/2;
	var positionOptions ='width='  + popupWidth + ',height=' + popupHeight + ',top=' + topPos + ',left=' + leftPos;

	if( options != '' )
	{
		options = options + "," + positionOptions;
	}
	else
	{
		options = positionOptions;
	}

	window.open( url, target, options );
}