How to check all contents of a type?

Hi,in my drupal's page I have a content type called "event", this content has a CCK date field.
I want to make a triggered rule, to check if those date fields have expired.
I tried to do it when the "execution of cron" and then .... I couldn't load all the contents of a specific type, and check that cck value (with a numerical comparision or whatever) for unpublishing them.

How can i do it?

(I don't want to use the node expire module, because that module uses a specific amount of time [30 days, etc] and I want users to put the date they want when creating "events")

Thanks for your help.