Hi,
instead of using an ODBC connection you should remove the link to the external database and bind it with a DSN less connection like Micrsoft has shown here:
http://support.microsoft.com/kb/892490With this you don't need any local ODBC connection on the computer and it will never again asking for a password (the same issue comes up when connecting to for example a SQL Server with ODBC).
Cheers,
Christian