How they have done it?

I usually go to Extreme arena which is nearby my college(Hansraj College) to play Counter Strike . I was really surprised at looking at their Opeating System. i didnot understood which operating system is it? When i reboot their system i got to know that it was Windows XP ..... They might have customised it! I want to know how they did it! :-D

**i55.tinypic.com/qzmc8p.jpg I am attaching a screen short *i55.tinypic.com/qzmc8p.jpg

You can easily narrow down to the Operating system within couple of seconds.

but how?

Look at the taskbar and for sure its windows.

usually all softwares can be identified by going to Help > About

Please can you tell me the method how they have done it Thanks in advance!

Right click on the green Icon in the system tray (near the time) and you should be able to know the name of the program, unless it is password protected or something else.

The Green Logo in the SysTray is Skype.
The procedure is simple, change the Start menu button logo. There are lots of utils available for that or simply use Resource Hacker and do it on your own. And then there is an application without the standard Title bar, very easy to make on VS.
I can bet they have disabled Task Manager and regedit so that people dont fiddle around with them and break out of this program.
Must say, nice idea by them.

I think it is just a full screen application custom developed by extreme arena people. i do not know why OP wants such a desktop for him because there are numerous other methods to have beautiful and useful desktop (e.g. Object Desktop etc.)

just a html file on startup and everything is blocked up taskmanager regedit and startbutton edited. i bet you can make far better customized desktop then this one.

if you want full freedom of customization, better use linux

Yup.. as a desktop replacement it is a sad option to choose. Please choose something better. IMO Object Desktop is a good option. Or Linux is even better. I am currently using Ubuntu 10.10 with GLX-Dock n Compiz Fusion and don't feel like using my Windows OS ever again... Extreme customisability on the desktop n everywhere..