[Moved the discussion to Photoshop Forum]
HansV, Not sure why are you actually trying to covert D800E nef file into Raw format as it can be used in ACR 6.7 and above used by PS CS5 or later.
In case you still want to convert your nef file into DNG, then you can use the below link.
You can't convert a RAW image (like a NEF) into another RAW image. The Adobe RAW is not the same thing.