//opens a new window
function openwindow(purl, pwidth, pheight)
{
	var scrx = (screen.availWidth - pwidth) * .5;
	var scry = (screen.availHeight - pheight) * .5;
	var features = "toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=0,width=" + pwidth + ",height=" + pheight + ",left =" + scrx + ",top =" + scry;
	window.open(purl,'',features);
}