Changing password of user can be done throught OWA.  If you are running Exchange 2007 environment on Windows 2007 with IIS 7.0 and also has Exchagne 2003 users then changing password throught Exchagne 2007 OWA would not be possbile you will get “404 page not found” Error message.

 As The Change Password feature in Exchange Server 2007 Outlook Web Access does not require the IISADMPWD functionality.  IISADMPWD functionality is used to change password in Exchange 2003 servers. 

Work around solution

1. When user is in inside office network then he/she can access OWA throught http://exchnage2003servername/exchagne/username

2.  a. Create the appropriate IISADMPWD folder and virtual directory on each Client Access server
b. Change the registory in Exchange 2003 backend serves – Click Start -> Run -> type regedit -> ok
c. Expand to the this path HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeWeb\OWA
d. Right click and create new DWORD with the name Disablepassword and set value to 0
e. On each Client access server, open IIS Manager, and then select Web Service Extensions.
f. In the result pane, select Active Server Pages, and then click Allow.

Reference Page : http://technet.microsoft.com/en-us/library/bb684904.aspx