Import the .nif to blender, edit it how you want, make the uv map fit your texture, export as .nif, open one nifskope with the original and another with your own, copy your nitristripsdata block over the original, make sure the two flower things match you textures, and make it the same position as your own and save it as a new 1 then change a statics model to that of yours.
Im not good at explaining. Good luck.
No... no.... just no...
That is old OLD information that is only still applicable to a very few things like weapons.
When you import the nif, the UV map is already there, no need to change anything for a simple retexture. The collision is also there, so if you are editing the mesh, you will need to also edit the collision to wrap around the new table shape.
If you are unsure as to how to manipulate the table, I STRONGLY suggest you start with some blender tutorials, as it would be really confusing for anyone to try and explain what to do to you.
If you need help with collision, there is this video I made
http://www.youtube.com/watch?v=AD4uywa1-pE
It assumes you know your way around blender, so id you don't then dont bother till you do.
@Miaximus: That video and http://www.youtube.com/watch?v=x6yixfbbGr4 one can be added to the list, duno if you have an update list or something to give to GStaf for updating the pinned thread.