I have been looking through the free 3d models resources on the internet. I have found some which come with .jpg textures and are UV mapped already. I tried attaching the texture and setting draw type to textured and then exporting as a nif. But Nifskope does not show the model as being textured.

How can I do this properly?

I think I may have figured it out. I set the Map Input for the material to UV. Then when I exported as a NIF it appeared with UV and texture !