I don't know for sure, but I'm guessing the 2004 stuff would fit the NX5. I've fitted one to my '92 RS250 (NF5) and this is what I found.

Front fairing: You will need to replace the top fairing mounts with TZ250 items. The std RS items are to short. You will also need to fabricate something to extend the front fairing stay (clock mount) as the nose is longer than the NX5 model. A couple of people here in the UK supply this stuff, check out www.iane.co.uk

Seat unit: The principle difference is the seat unit mounts to the sub frame vertically, rather than horizontally. Check out the image and see what I mean http://www.airtech-streamlining.com/images/10RS2503~1.JPG. I've found, or rather WayneNSR found that we also need a third bolt to the sub frame just in front of the tank. I just fabricated a few brackets from ali to do this.....not a pretty job, but then one can see it.

Good luck!