I have intel 945 motherboard with opensuse 11.1. While as normal user fully functional graphical desktop is achieved, on changing user to root, I get a black blank desktop with curser and nothing working. Please help

Root isn't supposed to log in graphically. It's a security risk and completely unnecessary. You should always log in as a regular user, then run root commands from a terminal using su or sudo. Most distros disable the ability to log in to a gui as root by default.

If you need to run a gui program as root, you can use gksu or gksudo (if running gnome), or kdesu (in kde), to launch the program. I'm sure there are other similar options also available.

You can also configure your x-server to allow root to directly launch gui programs. This has been covered many times, so please try a forum search if you want to set it up.

Most distros disable the ability to log in to a gui as root by default.
But this problem occurred only recently.
Now I have rectified the problem by disabling autologin feature.
Now I want to know the exact reason of this problem and whether I should enable autologin feature again?
And what is the advantage of dual logging (root/normal user) in a single user computer?