Overloading Subscript operator

What I am trying to achieve here is depicted in the small program
below.

// Wrapit.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <map>
#include <list>

using namespace std;

class A
{

 private:
   string a;
   string b;
   string c;
 public:
   A(){}

};

class B
{

  private:
  string a;
  string b;
  string c;

  public:
    B(){cout << "B constructor is being called \n";}
};

class C
{
  private:
    map<string, A *> aobj;
    map<string, B *> bobj;
  public:

  C(){cout << "Constructor of C called \n";}

  template <class T>
  T& operator [] (string key)
  {
     cout << "Operator [] called \n";
     return new A(); //if the key has a particular text in it return
new A
                     // otherwise return new B();
  }

};

int _tmain(int argc, _TCHAR* argv[])
{
    C c;
    c["abcd"] = new A();
    c["efgh"] = new B();

    return 0;
}

Obviously the above program will give you compiler errors.

I am trying to put a wrapper around the maps. And the insertion to the
maps is done through an
(eg . c["abcd"] = new A()) overloaded [] operator. Further I want to
use just one [] version of the function, but inside I will determine
whether I should return a new A() or a new B(). The string I recieved
as argument will have enough information for me to decide which object
to be returned. How would i do it.

My environment: VS2003 on Windows XP.

All your helps appreciated