<script>
function popitup(url) {
var w = 600;
var h = 400;
var l = (window.screen.width - w) / 2;
var t = (window.screen.height - h) / 2;
newwindow=window.open(url,'newwindow','height='+h+',width='+w+',left='+l+',top='+t+''); if (window.focus) {newwindow.focus()}
return false;
}
</script>
<button onclick="popitup('http://google.bg');">shtrak</button>