[nerbert]

Suppose you have someting like this:

<input type="text" id="countryname" />

<input type="submit" value="Submit" />

Add an onclick to the submit button like this

<input type="submit" value="Submit" onclick="encode()" />

<script type="text/javascript">
<!--
        function encode() {
               var counrtyname = fetch_object('countryname').value;
               countryname=PHP.urlencode(countryname);
               fetch_object('countryname').value=countryname;
        }
//-->
</script>

I think that would do it.