It’s surprisingly simple. Here the major steps:

1. Setup basic Drupal 6.2 installation aside of Joomla installation. You only need the Joomla DB for the conversion and can delete the files if you want.

2. Open Drupal Admin Area, go to Administer->Site building -> Modules and enable the Profile module by enabling the checkbox then hitting save.

3. Download http://drupal.org/node/249643 and copy it to your modules folder (eg. sites/all/modules). Use the same method as described in 2. just with the new conversion module. A new admin menu entry will appear after you enabled the conversion plugin.

4. Click the new “Import from Joomla” menu entry on the admin menu and enter your Joomla database access informations.

Now start the conversion and things should run through. The module was originally written for Joomla 1.0.6. but I used it with Joomla 1.5 and it worked fine.