I can hardly help with DCOM, but there's another approach: HTTP in case you have the IIS running on a computer in your LAN.

Place and register on this computer the DLL managing the passwords. Definitely such DLL can be written in FoxPro and addressed directly (ISAPI) from remote computers. Otherwise an ASP page can be used to create an instance of this COM class and return results.

It's easy enough to initiate HTTP request and obtain response using pure FoxPro code, especially on WinXP/2K/2003 computers.