<img src="test.jpg" href="javascript:winopen('http://site2');winopen(http://'site1');">
or
<img src="test.jpg" href="#" onclick="winopen('http://site2');winopen(http://'site1');return false;">
<script>
function winopen(url){
window.open(url,null,"height=400,width=400,status=yes,toolbar=no,menubar=no,location=no");
}
</script>