thank you so much for the Moodle 1.x -> 2.x conversion script !
In the latest version of the HotPot module (for Moodle 2.x) I have removed the "sourceitemid" field, so we don't need to worry about that field any more. I have some good ideas about how to set the "sourcetype", because the "hotpot/db/update.php" script also does that.
I am not sure yet what we need to do about the source file itself. As you know in Moodle 1.x the file is a seperate file on the server's file system, but in Moodle 2.x it needs to be imported into the Moodle database. Therefore, we will have to find a way to check if the file is included in the Moodle 1.9 backup file, and if it is we need to extract it and convert it to the Moodle 2.x format. Once that is done we should be good to go.
I will investigate further in September after I get back to Japan from my current trip to EuroCALL in Nottingham, UK.