Can't open NEF files on Photoshop CS2

This may seem arcane but I can't open the NEF files a friend sent me, shot with his Nikon D200.

I've been using CS2 for my Canon 30D but completely forget how to get the plug-in and install it to make the NEF's work.  I know it should be easy but I'm forgetful.  

Any help would be greatly appreciated.

Kind Regards,

Joel

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