I am using linux os, can any one say how to create it using gimp.. realy i like this tutorial..
It's do-able ....
Make a circular selection and fill it with the colour of your choice. Then make surfe you select none.
Then use the scissors tool to cut, - the scissor tool isn't necessarily easy - I used view grid and snap to grid and increased the grid resolution to get the cut I wanted. There may be other ways to make that selection.
Then just use the gradient tool and the standard drop shadow Script-Fu extension typically installed with the GIMP.
Nothing here that can't also be achieved with the GIMP.