function centerWindow(windowWidth, windowHeight) {
	var retval;
	retval = "top=" + ((screen.availHeight - windowHeight) /2) + "px,";
	retval += "left=" + ((screen.availWidth - windowWidth) /2) + "px,";
	retval += "height=" + windowHeight + "px,";
	retval += "width=" + windowWidth + "px,";

	return retval;
}

function standardPopupFeatures(windowWidth, windowHeight) {
	return "scrollbars,resizable,toolbar=0,status=0,menubar=0,dependent," +  
		   centerWindow(windowWidth, windowHeight);
}

function showHelp(url,target,windowWidth,windowHeight) {

	if (!target) target='_blank';
	if (!windowWidth) windowWidth=580;
	if (!windowHeight) windowHeight=750;
	
	var features=standardPopupFeatures(windowWidth, windowHeight);

	return window.open(url, target, features);
}