This is twice in a matter of a couple of days that the old myth of duplicate content has arisen. It's still a myth: Duplicate content summit at SMX Advanced By Vanessa Fox Matt Cutts: Supplemental vs. Duplicate Content Google Hell? By Matt Cutts Tue, May 1 2007
minstrel is right it's much less related to duplicate content and much more related to inbound links and site structure. If you have not already done it I suggest making a sitemap and submitting one to webmaster tools but make sure you have a decent navigational structure first. This means internal links matching up to the importance of the page, a 5th level article hosted on your site should have 2 or 3 internal passing it PR, not 50. When I recently worked on a client site simply changing their nav structure and resubmitting sitemaps got them about 60 places in the SERPs and a bunch of pages out of supplemental. They will probably get a PR increase too but they missed the last update. When building links target the home page and 5 top category pages for a month or so then expand targeting a few more deeper pages. The PR and link juice will filter down and hopefully imrpove things for you.