I recently ran into this issue when trying to upgrade a Joomla 1.5.23 site to 3.3. Here are the steps I took.

  1. Installed a local version of the site.
  2. Installed jupgrade
  3. Installed Admin tools
  4. Enabled MOOTools.

When I ran jupgrade it would download Joomla 2.5. At the end of decompressing the files there would be an error of “unable to find zip”. I used AdminTools and set the permissions of the tmp folder to 777 temporary. Ran jupgrade and everything worked perfectly.

For more info on how to upgrade your Joomla 1.5 to 2.5 successfully I have posted more details here.

http://blog.grimeymedia.com/jupgrade-migrating-undefined/

and

http://blog.grimeymedia.com/migrating-joomla-1-5-to-2-5/

And this article was a help.

http://wiki.redcomponent.com/index.php?title=jUpgrade:The_migration_process