No category ID in wp_posts?

Hey, I’m trying to do a quick little plugin that will email out a list of the posts from the last week to users.

But I only wanted to send posts from certain category, not all of them. So I looked in the wp_posts table, only to find out that the post_category field is all set to zeros. Why is this? How can I specify posts from different categories when doing this, if there’s no field setting them apart from eachother?

Edit – on doing a little more searching, I found that this field is obselete, left over from a legacy version, and that they are now handled in the wp_post2cat table. I think I can handle it now with this info. Thanks anyway, problem sovled!