Mike, one way to do it is to create a new thread topic, and expand the "Additional Options" thinger at the bottom, and check the box next to "Announce Topic", since you're an admin. When you submit the thread, it'll ask you for your password (to confirm you're an admin), then give you a list of membergroups to announce the topic to by e-mail. Select all the ones that apply, and fire away.
-BP