var target = "blank"; 
function jump(){ 
var url = document.form1.select.options[document.form1.select.selectedIndex].value; 
if(url != "" ){ 
if(target == 'top'){ 
top.location.href = url; 
} 
else if(target == 'blank'){ 
window.open(url, 'window_name'); 
} 
else if(target != ""){ 
eval('parent.' + target + '.location.href = url'); 
} 
else{ 
location.href = url; 
} 
} 
}