Limit post display to a single category

I am finishing development of a multisite for a crew organization that maintains separate sites for its mens and womens teams... On the home page of each of those sites is a nice widget that displays all recent posts by the category "announcements". I have a private community site that has BuddyPress and I would really love to display the posts with category "announcements" only in a widget on that site homepage. I have the post indexer installed and network enabled, and I can get all posts to display - but that's way too much.

How can I get granular and limit only to specific category names or ids?

If I should be using one of the other plugins to accomplish this, please advise.

Thanks!