Forum Moderators: Robert Charlton & goodroi
What you can do is use a 301 permanent redirect to send requests for the old urls to the best match out of your new urls. This also transfers any backlink power you may have already built.
You might find some help in this thread: URL structure redesign [webmasterworld.com]
That thread and other key discussions are available in the Hot Topics area [webmasterworld.com], which is always pinned to the top of this forum's index page.