function popUpSlideshow(URL) {
var slideshow_width = 650
var slideshow_height = 550
day = new Date();
id = day.getTime();
eval("page" + id + " = window.open(URL, '" + id + "', 'toolbar=0,scrollbars=1,location=0,statusbar=0,menubar=0,resizable=1,width='+slideshow_width+',height='+slideshow_height+'');");
}
<!-- Begin
<!-- NOTE: If you use a ' add a slash before it like this \' -->
document.write('<a href="javascript:popUpSlideshow(\'slideshow.html\')" class="navheaderon">Slideshow</a>');
//  End -->