On Thu, 2010-05-27 at 15:39 +0530, Santhosh kumar wrote:
> Oh...K.Thanks...I think now it is installed.But when I run
> 
> $roscore
> ImportError: No module named msg   //Error shown
> 
> $rosnode list 
> ERROR: Unable to communicate with master!  //Again Error
> 
> i am confused......!Whether there is error in installation.????

You probably need to compile ROS.
Thy this at the command line

$ rosdep install ros

Followed by
$ rosmake ros

Then roscore should work...

Also I strongly suggest doing the tutorials. 
http://www.ros.org/wiki/ROS/Tutorials

They might seem a little boring, but the reason why you should do they will be clear later.