@vasanth: And it would be better if you read the post instead of pointing him out to such a solution. He clearly mentioned that he was trying to activate Windows, not crack it.
@Ravindra: Be warned that if the configuration of the PC does not match that of your uncle's (in case you haven't bought the PC too) then activation would be unsuccessful and you would be required to contact Microsoft TechSupport to activate your copy of Windows XP. In case you cannot get your line working soon enough, I would highly recommend that you choose the Activation over Telephone method and then speak to TechSupport (+91 11 629 2640) in order to transfer ownership of the OS to your name as well as activate it for your PC. This way, you can give the Installation ID over to the representative and get the 42-digit Confirmation ID and then activate Windows XP without having to go online.