You don't get penalized for duplicate content. There only is duplicate content filtering.
You get penalized for linking to sites using unethical practices or for practicing them, too.
To avoid being flagged as duplicate (even with republished articles), you may want to get more links from trusted websites and use as much unique content as possible (meta tags, other page blocks - news, related articles, recent articles, etc). This won't help with block analysis, of course, but it's a good start.
Here's a piece on
Microsoft duplicate content filtering - it can be applied to other search engines as well.
First of all, you should consider the editorial quality of your articles.
Secondly, you may want to pick a topic of your directory, otherwise, you'll be just another article directory out there.