Try changing the line in fedora-xboard.desktop that reads Categories=X-Fedora; to Categories=Game;X-Fedora;
then run update-desktop-database
All this needs to be done as root
If this works (which it should), I'd suggest raising a bugzilla report on that, so that the maintainer for that package in Fedora Extras can fix it and get an update pushed out.
Paul.
