<style type="text/css">
span{border:1px solid red}
</style>
 
<script type="text/javascript" src="http://code.jquery.com/jquery-latest.js">
//jQuery inladen
</script>
 
<script type="text/javascript">
function roep(wattuh)
{
    alert(wattuh)
}
</script>
 
<script type="text/javascript">
$(document).ready(function()
{
	$("#span_1").dblclick(function() 
	{
		var inhoud = $("#span_1").html();
 
		//***********BEIDE OPTIES GEVEN UNDEFINED.....????*************//
 
		//var textveld = '<input type="text" id="input_span_1" value="'+inhoud+'" onkeyup="roep('+$(this).val()+')" />'; 
		var textveld = '<input type="text" id="input_span_1" value="'+inhoud+'" onkeyup="roep('+$("#input_span_1").val()+')" />'; 
 
		$("#span_1").html(textveld);
	})
})
</script>
 
<span id="span_1">1</span>

var textveld = '<input type="text" id="input_span_1" value="' + inhoud + '" />';
 
                $("input[id=input_span_1]").live('keyup', function() {
                    roep($(this).val());
                });