?php  echo'<form method=post><select onChange=MM_jumpMenu(parent,this,0) >';
while($glavsklad=mssql_fetch_array($glavsklad_result))
{
echo' <option value=www.fg.ru selected >'.$glavsklad[ 1 ].'</option>';    
}
echo'</select></form>';

http://skaldi.php?id_nom= 1 

<script>

var script_addr = "http://www.asd.ru/addskladiform.php";

var script_var = "id_sk";

function mySklad(cb) {
	for(i= 1 ;i<cb.options.length;i++) {
	    if (cb.options[i].selected==true) {
	        document.location= script_addr + "?" + script_var + "=" + cb.options[i].value;
	        break;
	    }
	}
}
var scr=document.location;
var varscr="id_prep";

function myprep(cb) {
	for(i= 1 ;i<cb.options.length;i++) {
	    if (cb.options[i].selected==true) {
	        document.location= scr + "&" +varscr + "=" +cb.options[i].value;
	        break;
	    }
	}
}
</script>