d6 port ?

jup... i also would like to try a D6 version. cool module idea!

The menu system changed as far as i know. As far as i can see the following functions are involved:
http://api.drupal.org/api/function/theme_menu_item
http://api.drupal.org/api/function/theme_menu_tree
http://api.drupal.org/api/function/menu_tree (< i guess this changed a lot?)

bedlam, do you have any experience with D6 yet... any chance for a port to 6?

I won't port the module until I have cause to work with Drupal 6 that needs this sort of menu function--there is a project coming up that might require me to build a Drupal 6 version, but I have no current deadline for finishing that work (and I don't know if time/budget will permit modifying this module).

As pointed out in another issue here, there's a module that is, at the moment, quite similar to this one, and that's available for Drupal 6: http://drupal.org/project/menu_block. If you do need Drupal 6 compatibility, and you don't need unique ids on list items or the ability to change CSS class names from the block administration page (these are the main differences between the two modules at this moment), it looks like a very good choice.