The variables are:
screenX=pixels from the left for Netscape 4+
screenY=pixels from the top for Netscape 4+
left=pixels from the left for internet explorer 4+
top=pixels from the top for internet explorer 4+
Example code:
<a href='#' onClick=" opt='height=250, width=600, menubar=no,statusbar=no,titlebar=no, screenX=200, screenY=100, left=200, top=100, resizable=no,scrollbars=no'; var remote=open('http://ww.AdFos.com' ,'MS', opt ); return false;">AdFos</a>