There are a great number of stellar wallpaper images available for the Macintosh. It isn't possible for us to know which one you are referring to.
However, it is quite likely that the image you are referring to is one of these:
http://hubblesite.org/gallery/wallpaper/
In astronomy - there does not appear to be a nebula with that name.Other options could be:The Green Leopard Plague which won the nebula awards.A fictional wallpaper made with photoshop and used in Mac OSX
"The Crab" is a nebula.
By getting a Windows machine
The crab nebula.
can i put my name on computer wallpaper and play music
A nebula. That's composed mostly of hot gasses. Hence, the name. Hot nebula.
protostar or nebula
Galaxy
Swan Nebula
wallpaper ----
your mam
The Horsehead Nebula can be found in the constellation Orion. Its name comes from its resemblance to a horse's head. The Horsehead Nebula was first discovered by Williamina Fleming in 1888.