Venky,

(assuming you haven't succeeded in the past week... if you already have,
please post the methodology here).

add the ip and gateway details given by sify to the file /etc/network/interfaces.
(man /etc/network/interfaces in case of doubt).
However, there's something sify specific here. There's something to do with
a MAC address (http://en.wikipedia.org/wiki/MAC_address). Something has
to be done about this one too. Please check this out and do let me know if
you succeed. (I am going to try it out later in the evening).

Hope this helps.