var winxpos = (window.screen.width);
var winypos = (window.screen.height);
var newwinxpos, newwinypos;

if (winxpos > 810) {
newwinxpos = (winxpos-760)/2;
newwinypos = (winypos-580)/2;
window.moveTo(newwinxpos,newwinypos);
}
else {
window.moveTo(20,0);
}