Event + Category + Multiple category selection

Hello,

I have site where Events and Classified are categorized by location (Country -> State/Province -> City), so people can view results relevant to their area (a la Craigslist.org)

I have Category and Active Select module create the dropdown menus with the categories when I edit a node (Event/Classified - see http://drupal.org/node/74747).

Then to display the Classified ads relevant to a particular location, I just go to the node of that category (ex. /united-states/california/berkeley), and I see all the classified listed below. Both input and output are very neat and consistent.

I would like to port the input into the Event calendar display/output, so when I see the calendar, I can choose Country, which will populate State/Province, which in turn will populate City - just like on the input.

Here (http://drupal.org/node/147437) someone attempted something similar, and killes pointed them to http://api.drupal.org/api/head/file/developer/topics/forms_api.html and to "use hook_form_alter to change event_taxonomy_filter_form".

In template.php I set up a function phptemplate_event_taxonomy_filter_form($curterm, $autosubmit), and it overrides the default drop-down menu, but I'm a bit at a loss about where to go from here.

I'm hoping to get some feedback on how to port the category input form to the event display output.

Any suggestions or ideas are very much appreciated.

Thank you,
Andrey.