first of all, save it as msn.provider and msn.service, not anything ending at .xml
Use for saving the normal windows editor / notepad. Not wordpad, word or something else, just plain plaintext.
It is after all a plaintext file that's using XML notation. Nothing more or less.

msn.provider goes to /usr/share/accounts/providers/
msn.service goes to /usr/share/accounts/services/

Beware that linux is case sensitive so Msn.service is another file than msn.service (see the "M" vs "m").