Listo ya resolvi...
Código PHP:
Ver original<html>
<head>
<?php $grupos= 5;?>
<script language="JavaScript">
function suma1(){
var res = new Array();
var f;
var j;
var res2 = 0;
for(f=1;f< <?php echo $grupos + 1; ?>;f++){
var v;
res[f] = document.getElementsByName(f)[0].value;
}
for(j=1;j < <?php echo $grupos + 1;?>;j++){
res2=res2 + parseInt(res[j]);
}
document.getElementById("SUMA").value=res2;
}
</script>
</head>
<body>
<form name="form1">
<?php for($i=1;$i <= $grupos; $i++){?>
<select name="<?php echo $i?>" type="comboBox" onchange="suma1();">
<?php for($j=1;$j<=$grupos; $j++){?>
<option value="<?php echo $j?>"><?php echo $j; ?></option>
<?php }?>
</select>
<br><?php }?>
<input name="SUMA" type="text" id="SUMA" size="15" value="" />
<input name="RESTA" type="text" id="RESTA" size="15" value="" readonly="readonly" />
</form>
</body>
</html>