I was able to go from Moodle 1.9 to 2.0 via these steps, long ago. From there I gradually worked up the ladder of Moodle versions.
Halverson
From my notes:
**************** How I migrated from Moodle 1.9 to 2.0 **************
----------------- Key helpful web pages -------------------------
Moodle 1.9 to 2.0 format conversion:
http://www.moodleinschools.org.nz/courseconverter
Issues with files in moodle 1.9 to 2.0 migration
http://docs.moodle.org/20/en/coursefiles2
About broken links:
http://classes.sscnet.ucla.edu/docs/Resurrecting_broken_links_in_a_restored_Moodle_site
------------------ Step-by-Step ---------------------------------
1) Because of a 32 MByte limitation, I get rid of big files from my course.
This is necessary because of Moodle 1.9's inability to handle "just some" files. (See "issues with files" link)
2) I create a backup of my course. I include everything.
3) I download the backup zip file.
4) I go to the Moodle 1.9 to 2.0 format conversion site http://www.moodleinschools.org.nz/courseconverter and
upload the zip file. A few minutes later I receive the converted file via email. (Change/rename.mbz to .zip)
The next two steps were needed for my physics migration, due to previous problems. They were not needed for the chemistry moodle.
5) If needed: Seperately upload question banks (For quizzes and question banks, use the moodle xml format!)
6) If needed: Re-link images