How to make a skybox/dome from a panoramic image

Ok, so I followed the skybox tut with pretty good success >> TUT LINK <<
See how they use 2 images, the sky, and the ground; and the sky one is like a fisheye view …

Well I want to just use this picture for my skybox, how do I do it, with only this one picture?

Is there a way?
Do I have to slice the ground portion of it off , and then take the sky portion and convert it to the fish eye looking type of picture (is that even possible) ???

Help :confused:

Thank you