@Professor Anthrax
I'm clearly no expert on mumble, but anecdotally; when I ran mumble NOT as an administrator, I got the same lengthy server list as you did, with nothing FH2 related to be found.
However when I ran as admin, it automatically when straight to the FH2 lobby, and automatically set me up with the squad once I was on the WaW server. So running it as admin seems crucial.
There does seem to be a way to do that in XP, I'd just google it.