Did you found anything? I'm in pursuit for such script too... I found: Fudforum (forum with nntp support), PhpBB (there is "newssync" hack for this), Vbulletin (paid software ~$150, there is free mod for NNTP), Newsbox (found at Hotscripts, $50, dedicated for Usenet).
I'm currently testing two first solutions, but they are not good idea if you want to publish many groups (or whole usenet). I don't own Vbulletin so I have no idea how does it's NNTP plugin works, but it's probably similar to the free ones. Newsbox script looks quite good, but it doesn't include "flat" view, only threaded one, where you have to click each message to view it... and this sucks (author of the script told me that he can add flat view for $30). Besides that, I have no idea how reliable it is.
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