Sharepoint - 如何将子站点中的公告聚合到主站点上

I am new to Sharepoint (WSS 3.0) and have the task of creating a company intranet. This site will have a number of sub-sites - each owned by a different department. Each of the sub-sites will have an 'Announcements' webpart on their top-level page.I am new to Sharepoint (WSS 3.0) and have the t