Is it possible for Tixati to finish downloads started by another p2p program (for example, uTorrent)? Or should we just finish what downloads have been started with our previous p2p program and start new ones with Tixati if we download it?

uTorrent has an option to append files with the .ut! extension after the regular file extension. I should note that this is NOT enabled, all files are in their original format and some are accessible after they have reached a certain percentage.

Thanks in advance.

Yes, it is possible. You have to:
1. add a torrent file
2. point to location of partially downloaded file or folder
3. click stop - it's safer to add the task stopped
4. right-click > Local Files > Force Check
5. start the download after check is complete