There is an extensive amount of info on raw conversion in this site.
http://www.dpreview.net/
Try a search in the retouching forum or the Nikon or Canon Forum for Bibble, Breezebrowser or Capture One.
They will all do Raw conversion for D-70 files. Each have their own devotees. They are all very good, each with their own workflows and enthusiasts. Adobe CS does do raw, as does Adobe Elements 3. I use Capture One and find it to be excellent but each of them have trial downloads. Give them a try.
Hello again, I reread your post:
"The facility I really need is to convert the NEF files into a format PhotoShop 6 supports, such as TIFF and JPG (I realise you can take JPG when you take NEF, but I\'d rather just dump the NEFs in, and then convert as and when needed).
The programs that I mentioned above are not simply to convert NEF to jpeg or tiff. You would be missing a lot if that is all that you would use the program for. They are designed to allow complete processing of the raw image to a finished image. IE, white balance, colour correction, saturation, exposure correction including curves, contrast and finally sharpening.
Capture One has come in for a lot of criticism for their customer service but in spite of that the product is good enough for a lot of people to hold their noses and stick with it anyway. I am one of those. It is an excellent program. I am using it to do my raw files from a Canon 20D and I am a believer.
I\'m pretty sure that PS 6 will not handle NEF, I think you would need PS CS.