Integrate with Event module

That would indeed be nice. I've added to my feature-list!

coming from http://drupal.org/node/141411 i second this feature request

:-) I'll also vote for this one! I've been trying to figure out how to do this myself and it's been getting messy.

on d6 this also is missed a lot :(

Modify the event view and add the birthday field to it:

Create a custom module:

function custom_love_views_query_alter(&$view, &$query){
    if ($view->name == 'YOUR_EVENT_VIEW') {
        $where_clause="MONTH(YOUR_BIRTHDAY_FIELD) = MONTH(curdate()) AND DAYOFMONTH(YOUR_BIRTHDAY_FIELD) = DAYOFMONTH(curdate())";
        $view->query->add_where('birthday_filter', $where_clause);
    }
}

I didn't test it but this should work on D6 i have no experience on D5...

Should go into 7.x-1.x first, might be backported to 6.x and won't happen for D5 (unless someone writes a straight forward patch).

Postponed at least until Event has a stable release.

Shouldn't this be for entity registrations now? It can be considered a replacement of event.

sorry, my bad, thank you for the tip.
won't happen again :)