how to Specializations of function Templates or Overloading Function templates with Templates ?

#include <stdio.h>

template<class T>
class TpHello
{
public:
 int GetHash(){return 0;}
protected:
private:
 T a;
};

template<class T>
int HashKey(T key)
{
 return (int)key;
}

//Specializations of function Templates or Overloading Function templates
template<class T>
int HashKey(TpHello<T> key)
{
 return key.GetHash();
}

int main()
{
 TpHello<int> tpInt;
 HashKey(tpInt);
 return 0;
}

compile error in VC6
--------------------Configuration: template - Win32
Debug--------------------
Compiling...
template.cpp
E:\work\hellotest\template.cpp(52) : error C2667: 'HashKey' : none of 2
overload have a best conversion
E:\work\hellotest\template.cpp(52) : error C2668: 'HashKey' : ambiguous call
to overloaded function
Error executing cl.exe.

template.exe - 2 error(s), 0 warning(s)

--
= = = = = = = = = = = = = = = = = = = = = =


                                  zhang
----------------------------
Co.: beijing lingtu
Ad.: beijing zpart
ZIPT 100094
MailTzhangzhigang@lingtu.com
MSN: recover_su@hotmail.com
Com.T http://www.lingtu.com/
         http://www.51ditu.com/
--------------------------