enlightenment
 

hi
i have 2 questions

1} what is enlightenment
2}what is meant by enabling enlightenment in gnome

Enlightenment is a window manager. You can look at the project's web page here.

"enabling enlightenment in gnome" would probably be someone's method of saying "replace your current window manager with enlightenment". Gnome is a desktop environment, and can work with pretty much any window manager. It's simply a matter of personal taste which window manager you use, and then taking whatever steps you need to tell Gnome which window manager to use when Gnome starts up.

thanks for the link

by default what windows manager does gnome(2.8) use.
andf how do i change the windows manager..
thank you

By default, GNOME 2.8 uses metacity, I'm not sure how to change it exactly but if you search I know there's plenty of topics getting around that explains it.