Hot to get Current user name using SPAPI

 This is so simple just need to follow step in correct way
<-----Start------------------->
<script src="/SPAPI_Core.js"></script>
<script src="/SPAPI_Lists.js"></script>
<script src="/jquery-1.4.1.js"></script>
<script type="text/javascript">
$(function (){
 var nameOnly = getCurrentUserName();
 alert(nameOnly);
});
function getCurrentUserName(){
// put path of user information list
var lists = new SPAPI_Lists('path for User information list is');
// put the id of user information list
var items = lists.getListItems('888216C4-B998-4889-91C2-16D68127010A','','<Query><Where><Eq><FieldRef Name="ID"/><Value Type="Counter">'+ _spUserId +'</Value></Eq></Where></Query>','','');
 if (items.status == 200)
 {
 var rows = items.responseXML.getElementsByTagName('z:row');
  for (var i=0; i<rows.length; i++)
  {
    return rows[0].getAttribute('ows_Title');
   break;
  }
 }
 else
 {
  alert("Error in getting user");
 }
}
</script>
<-----End------------------->

If you are getting any error then check ur linked file path.

Thanks