I have been looking at this too. I just started venturing into the world or RAW. I tried Photoshop, but my computer and Photoshop would not play nice together. So, I ended up getting PSPXI. Works fine on my computer, but I do not like the RAW conversion. I currently have a free download of Capture One. I really like the RAW conversion, but it does not offer much in the way of editing. And from what I have read, you should do most of your editing and then convert last.
Do you know the difference between Capture NX and Capture 4?