This is the banded Malabar Swallowtail or Papilo Liomedon. This is apparently a very rare species and is not sighted so far up north. What this means is that I am extremely fortunate to have taken this picture.
Edit - 21 August 2011
This is the Common Mormon or Papilio Polytes. Source: http://indiabutterflies.tripod.com/swallowtails/commonmormon.html