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Great information.  My understanding was always the same as Steve's .....it depends on the ratio of unique vs. duplicate content.  A while back, I had read that this ratio was something like 80/20 (duplicate not to exceed 20%).  However, I think I will make each piece unique for best results.

Is it possible for you to put that listing content in an image?  This would allow you to continue using indentical content on all pages.  However, the content in the image would not be searchable.  If you are just using this content for the user experience, that's fine.  If you want it indexed to add quality to the page, you will instead want to make each listing unique.

If you are looking for an open source solution, I recommend phpBB (http://www.phpbb.com/).  We have used it for a few years for our forum and I'm happy with it.