How can I convert Posts into Custom type posts?

I have a WordPress site that I just updated to 3.1. I want to make use of custom post types now, my question is how can I assign (transfer?) a post to a newly created custom post type ?

For example, all my articles (news, poems, ideas to change the world) are in Posts. Now I have created the custom post types News, Poems, etc. and I want to transfer my old posts to these new custom post types.

I hope this is clear enough, anybody ?

It seems that the easiest way is to do it manually in the DB. If you don’t have access to the DB, or if you don’t want to do it manually, you can install a plugin that will do it one post at a time, or a plugin that will bulk convert a lot of posts at once