If you move documents around without putting in a 301 (permanent) or (302) temporary redirect, Google thinks it's new content.   What this means is that google will continue to show your existing documents/links as viable pages as well as the documents found in the new area.  Since Google won't update it's index w/out those redirects, your old document links will 404, as opposed to gracefully redirecting.

You may want to consider looking at ifinity.com.au's url master product.  It can do pretty much everything I mentioned above.  Also, Bruce Chapman has done some amazing work with making DNN more SEO workable.  I highly recommend you check it out.

-- Scott Allender
www.scottallender.com