>Rick and Phillip, I'm using CS5 and was thinking if I bring >all NEF files into LR4, convert to DNG then it's a go. That's >what you are both saying, right?
Not exactly - but you can do that. It's a more simplified process to use the free, stand-alone DNG Convertor to create DNG copies of NEF files.
But yes, LR4 can convert to DNG through the File> Export (or Export with Preset > Export to DNG) command although that's not required to open a D600 NEF file in PS <CS5.5 with LR.
You can right click (Cntrl Click on Mac) and choose Edit In >Adobe PhotoShop or use the regular menu Photo> Edit In > Adobe PhotoShop CSX where X is your version, you may have to 'register' your PS app with LightRoom so it knows you have it (and you can register any other image editing app to appear in this menu as well)
BUT - if your version of PS is CS5.5 or earlier you will get a warning
"This version of Lightroom may require the Photoshop Camera Raw plug-n version 7.3 for full compatibility. Please update the Camera Raw Plug-in using the update tool available in the PhotoShop help menu" Cancel | Render Using Lightroom | Open Anyway
Despite the helpful hint to update, if your version of PS is CS5.5 or earlier you can NOT update to ACR 7.3. ACR 7.3 only works with CS6 and up. So if you select Open Anyway you'll get a PS error. But if you choose 'Render using Lightroom' then LR will render the NEF file, using any edits you've made in LR, into a .tif file and open that in PhotoShop.
I see nothing wrong with this workflow for 90% of photographers. It's what I do and I work full time with images and magazine production. But if you need the latest and greatest features and so on then the best option is to upgrade PS to CS6 or use the Nikon software workflow etc...