You can buy DS2 from FLipkart, game will be added to your Steam Account. You can buy the Season Pass from GG (right now
) - you will get a Steam code, which you can redeem at Steam. You can then purchase any other DLCs including future ones too.
Excellent guide to make Battlefield 1942 run smoothly on your ultra modern PC:-
Rage3D.com : Playing Battlefield 1942 in 2012 [ Introduction, resolution, FOV, AA ]
The game is still free at Origin, and will remain so until March 2013, after that... only EA knows. :
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