get all tags from category

i’m displaying all posts by category in my template and i was wondering:
is it possible to get a list of all tags used by that category?

i only found out how to make a tag-dropdown but it’s from all articles,
i couldn’t find out yet how to filter it by category – any ideas?

here’s the link
http://wphacks.com/how-to-display-wordpress-tags-dropdown-menu/

thx in advance

Late answer

There’s get_terms() here for that. No need for any custom queries.