HTML:
<a href="javascript:help('homehelp');">
<img src="../images/help.gif" alt="home" /></a>

JAVASCRIPT:
function help (tmpl_to_open) {
    window.open("http://foobar.com/instances/help?rm=sh&pg="+tmpl_to_open,"optional_page_name","scrollbars=1,location=0,directories=0,status=0,width=550,height=375,toolbar=0,menubar=0,resizable=0");
}