It seems to work like this:
InitialenRemote initiaal = null;
Context context = new InitialContext();
UserTransaction userTran = (UserTransaction)context.lookup("UserTransaction");
try{
userTran.begin();
String strInitiaal = initialenForm.getInitiaal();
Object einRef = context.lookup("Initiaal");
InitialenHomeRemote home = (InitialenHomeRemote)PortableRemoteObject.narrow(einRef, InitialenHomeRemote.class);
initiaal = home.create(strInitiaal);
userTran.commit();
}catch(Exception e){
userTran.rollback();
e.printStackTrace();
}