form.submit中控制。。。。
<html>
<script language=javascript>
function dosubmit(){
window.open('first.php?var1='+window.form.var1.value+'&var2='+window.form.var2.value);
window.open('second.php?var1='+window.form.var1.value+'&var2='+window.form.var2.value);
return false;
}
</script>
<form name=form onsubmit="return dosubmit();">
<input type=text name=var1><br>
<input type=text name=var2>
<br><input type=submit></form>