I want to know how to edit ubuntu,s kernal to change its desktop for multi desktop.
You don't need to hack the kernel to configure the desktop. Thank god Linux is more user friendly than that .
I'm not sure what you mean with "multi desktop" though... If you're using the default and latest ubuntu, there should be a desktop switcher in the lower right corner of the screen. See this screenshot, it's the brown square with three grey squares next to it. The brown square is the currently active desktop, the grey ones are the other three.
If you meant to ask how to get 3D desktop effects (XGL or AIGLX) (wobbly windows, the cube, etc etc), then I can't help you, because I don't use ubuntu or a 3D desktop. I'm sure someone else can help you though, but please first clarify what you want, so they won't be sending you in the wrong direction.
Welcome mabhana. I moved this topic from GetGNULinux.org support to "Software Support" forum as that's where it seems more appropriate. GGL forum is only for GGL site related discussions.
As for your question I agree with tbuitenh.
Just a note, maybe it's better not to move questions of new users until after they have been answered, otherwise the user might not be able to find the post.
Good point, though he didn't go through the forum index to post this. He used that "need help" link and the drop down box to select the forum.
So it doesn't seem to make much of a difference. The post is on the homepage and in the "new on forums" block.
Oh, I thought (s)he got in through some direct link from GGL.