I'm not sure if this is exactly what you need, and is not just a simple convertor, but I believe Qimage Pro will convert NEF format files to TIF format. We used to use this software at work, but we now use JPG format only on our new D1, and Photoshop CS.
Their software company is
here, but as I say there may be a much better solution elsewhere, and possibly a free one (Qimage is about $45).
Good luck
WP.