This can even be done client side, using javascript; something like so:
<scripttype="text/javascript">
function getArgs() {
var args = new Object();
var query = location.search.substring(1);
var pairs = query.split("&");
for (var
i = 0; i < pairs.length; i++) {
var pos = pairs[i].indexOf('=');if (pos == -1) continue;
var argname = pairs[i].substring(0, pos);
var value = pairs[i].substring(pos + 1);
value = decodeURIComponent(value);
args[argname] = value;}return args;}
var args = getArgs();
document.getElementById('frmSearch').src = args.resultsurl + '?'+ location.search.substring(1);
</script>