Quote: "I am still not quite clear what it is that you want to achieve, exactly."
So, I couldn't explain it well

Please take a look at this article:
http://www.cs.unc.edu/~ibr/other_pubs/schaufler_egrw97.pdf ~100KB
Quote: "What happens if your sphere is textured and you want to turn it in the scene"
hmm, the same thing as I wanted to rotate a billborad... I can't
Quote: "Do you mean that your sphere is in a fixed position in the scene"
Not necessarily in a fixed position, but it'll be facing the camera(or camera aligned) anyway.
Quote: "If I'm right then a shader solution seems to be a simple answer.

"
Well, I hope so

(then, how about depth buffer direct access problem in DBP?)
Quote: "It was suggested on a recent DBP thread that we ought to have a thread dedicated to shader challenges."
WOW, what a nice idea. I would love something like this. I'm looking forward to hearing from you guys, don't make us stand waiting... haha, a shader challenge thread, whoa, can't wait for that

(Start simple so we could have a chance to get envolved with it too!)
Quote: "Would you object if your problem was made one of the challenges?"
Object? haha, I would be grateful
Other names for depth-sprite are 'nailboard' and 'z perturbation' as far as I know
Thanks in advance
-Try