EDIT: I've found how: when I open the torrent, it asks me what the files I want to download are. I say 'none'. And then it puts itself to seed. But now there is a new difficulty: in the Trackers tab it says: Tracker status: could not connect to host tpb.tracker.thepiratebay.org.
In the same tab, and in the 'Tracker' window, there is only one item, namely 'tpb.tracker.thepiratebay.org/announce'.
When I press 'Update tracker' (with the tracker selected) nothing happens. Is there anything I can do?
a) Look for a new torrent tracker for the downloaded file. Use google; download the torrent and copy the tracker into the 'tracker' window as you have stated above.
b) Do not click 'Upgrade'. Just click 'Create' button at the bottom.
c) At the Upload list window right click the item and click 'Manual Announce'. Leechers should find your available file if not today in days, just leave your ktorrent running all along, you can click the taskbar icon to minimize it to the taskbar.
FYI: For the torrent handling there should be other downloaders available in your distro CD, where you may install 'bittorrent' or 'bittornado' which are simple to run. You can also find in the internet many other free like 'Deluge' which is really good, and 'Vuze for linux' too.
Good luck. Keep on seeeeeeeeding.