Here is the code I found on www.yvoschaap.com

<script>//script by http://www.yvoschaap.com//XMLHttpRequest class functionfunction datosServidor() {};datosServidor.prototype.iniciar = function() { try { // Mozilla / Safari this._xh = new XMLHttpRequest(); } catch (e) { // Explorer var _ieModelos = new Array( 'MSXML2.XMLHTTP.5.0', 'MSXML2.XMLHTTP.4.0', 'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP', 'Microsoft.XMLHTTP' ); var success = false; for (var i=0;i < _ieModelos.length && !success; i++) { try { this._xh = new ActiveXObject(_ieModelos[i]); success = true; } catch (e) { } } if ( !success ) { return false; } return true; }}datosServidor.prototype.ocupado = function() { estadoActual = this._xh.readyState; return (estadoActual && (estadoActual < 4));}datosServidor.prototype.procesa = function() { if (this._xh.readyState == 4 && this._xh.status == 200) { this.procesado = true; }}datosServidor.prototype.enviar = function(urlget,datos) { if (!this._xh) { this.iniciar(); } if (!this.ocupado()) { this._xh.open("GET",urlget,false); this._xh.send(datos); if (this._xh.readyState == 4 && this._xh.status == 200) { return this._xh.responseText; } } return false;}var urlBase = "update.php";var formVars = "";var changing = false;function fieldEnter(campo,evt,idfld) { evt = (evt) ? evt : window.event; if (evt.keyCode == 13 && campo.value!="") { elem = document.getElementById( idfld ); remotos = new datosServidor; nt = remotos.enviar(urlBase + "?fieldname=" +encodeURI(elem.id)+ "&content="+encodeURI(campo.value)+"&"+formVars,""); //remove glow noLight(elem); elem.innerHTML = nt; changing = false; return false; } else { return true; }}function fieldBlur(campo,idfld) { if (campo.value!="") { elem = document.getElementById( idfld ); remotos = new datosServidor; nt = remotos.enviar(urlBase + "?fieldname=" +escape(elem.id)+ "&content="+escape(campo.value)+"&"+formVars,""); elem.innerHTML = nt; changing = false; return false; }}//edit field createdfunction editBox(actual) { //alert(actual.nodeName+' '+changing); if(!changing){ width = widthEl(actual.id) + 20; height =heightEl(actual.id) + 2; if(height < 40){ if(width < 100) width = 150; actual.innerHTML = "<input id=\""+ actual.id +"_field\" style=\"width: "+width+"px; height: "+height+"px;\" maxlength=\"254\" type=\"text\" value=\"" + actual.innerHTML + "\" onkeypress=\"return fieldEnter(this,event,'" + actual.id + "')\" onfocus=\"highLight(this);\" onblur=\"noLight(this); return fieldBlur(this,'" + actual.id + "');\" />"; }else{ if(width < 70) width = 90; if(height < 50) height = 50; actual.innerHTML = "<textarea name=\"textarea\" id=\""+ actual.id +"_field\" style=\"width: "+width+"px; height: "+height+"px;\" onfocus=\"highLight(this);\" onblur=\"noLight(this); return fieldBlur(this,'" + actual.id + "');\">" + actual.innerHTML + "</textarea>"; } changing = true; } actual.firstChild.focus();}//find all span tags with class editText and id as fieldname parsed to update script. add ondblclick functionfunction editbox_init(){ if (!document.getElementsByTagName){ return; } var spans = document.getElementsByTagName("span"); // loop through all span tags for (var i=0; i<spans.length; i++){ var spn = spans[i]; if (((' '+spn.className+' ').indexOf("editText") != -1) && (spn.id)) { spn.ondblclick = function () { editBox(this); } spn.style.cursor = "pointer"; spn.title = "Click to edit!"; } }}//crossbrowser load functionfunction addEvent(elm, evType, fn, useCapture){ if (elm.addEventListener){ elm.addEventListener(evType, fn, useCapture); return true; } else if (elm.attachEvent){ var r = elm.attachEvent("on"+evType, fn); return r; } else { alert("Please upgrade your browser to use full functionality on this page"); }}//get width of text elementfunction widthEl(span){ if (document.layers){ w=document.layers[span].clip.width; } else if (document.all && !document.getElementById){ w=document.all[span].offsetWidth; } else if(document.getElementById){ w=document.getElementById(span).offsetWidth; }return w;}//get height of text elementfunction heightEl(span){ if (document.layers){ h=document.layers[span].clip.height; } else if (document.all && !document.getElementById){ h=document.all[span].offsetHeight; } else if(document.getElementById){ h=document.getElementById(span).offsetHeight; }return h;}function highLight(span){ //span.parentNode.style.border = "2px solid #D1FDCD"; //span.parentNode.style.padding = "0"; span.style.border = "1px solid #54CE43"; }function noLight(span){ //span.parentNode.style.border = "0px"; //span.parentNode.style.padding = "2px"; span.style.border = "0px"; }//sets post/get vars for updatefunction setVarsForm(vars){ formVars = vars;}addEvent(window, "load", editbox_init);--></script>

 The editable fields are then entered as follows

<span id="userName" class="editText">John Doe</span>

 If you manage to find out how to complete this in a Visualforce page, please let me know

Thanks!