If you've run into the error message KDEInit could not launch '/usr/bin/ktorrent' on KDE 4, you are not alone. It appears that this is a KDE Bug that should be resolved in a bug-fix update in the near future. This also apparently affects other applications besides KTorrent.
In my case, when I clicked on a torrent file, the error message cropped up, but the file itself was open fine ...