To answer your questions
1) i have tried with both default initial context as well as below settings
Hashtable env = new Hashtable();
InitialContext initialContext = new InitialContext(env);
2) am running single machine..ejb is deployed in ear within websphere and am trying to access ejb from custom user registry class
3) Do i need this jndi client jar library of Websphere ..Is this file present within websphere...I have not changed the classpath default settings? i am unaware of this jar.