You should be able to start it from the terminal by typing 'ktorrent <enter>'.
Getting the correct ktorrent.desktop file into /usr/share/applications should fix the xfce/Network menu issue, but I'm not exactly sure where the current ktorrent.desktop file is located. You could try a 'locate' to find the file, however you may want to update your system database with 'updatedb'.
# locate ktorrent.desktop
If you find that you already have a ktorrent.desktop file located in /usr/share/applications then the file probably needs to be edited to better fit XFCE. If you post the output from the locate command posted above plus the output from the following comment I'm sure we can help you get all fixed up; command 'cat /path/to/ktorrent.desktop' (/path/to/ should be replaced with the correct path as output by the locate command).
Hope this helps!