Well unless i don't understand the ktorrent architecture, you can't start it on boot, as it's a KDE4 only application, not a client / server piece of kit. You could start it when you log in to KDE (maybe automatically) after the boot has finished, assuming you are using KDE, which you may well not be, by adding to ~/.kde/Autostart.
http://itg.chem.indiana.edu/inc/wiki/software/168.html