Hey Thanks man,
I found and I have done it. I got the information from internet and already designed pins_arduino.h file. I just copied the text in separate text file in my laptop and then done as directed in other website. I do not have tested yet but I think it may work definitely. If any issues will be there related to this board.txt and pins_arduino.h, I will come to you back. ANyway, thanks a lot for helping me. Its too easy.
Thanks again.
Chirag
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Its late here at night and I will post it by tomorrow. But for your better start up, I have attached the Proteus 7.8 file and you can check it for schematic and the ports are same as ATmega128 in this ATmega1280. Anyway, you knows better than me. So I will not explain anything more. Please find the attachment.
Thanks.
Chirag