unable to change exchange password

My Organisation Use Exchange 2003 SP1 on Windows 2003 and clients access Through Outlook 2000/xp/2003.None of the clients are able to change their exhnage user password from client side. Computers are not joined to any domain. Exchnage 2003 with windows 200 active directory supports this feature if you add the Registry Dword TCPIPClientSupport under LSA.Is there any option which works with windows 2003?