To get the rank A you have to:
** Start the game in hard mode, no ranks for easy games
** NEVER EVER use a first aid spray
** Dont save your game more then 2 times, or else its no more A.
** Keep it quick, make sure your time is less then 1:30
** Dont shoot unless required
** Learn the meaning of the word dodge
** Never fight nemesis until its required
** Make sure that you take the right live decisions
** Make only the strong ammo via the reloading tool
** Green herbs only, but keep them to a limit too
** Skip every scene in the game, we dont have time to listen to anything
** Follow the given boss stratergies
** Run from hunters if possible
and the rewards when you get the rank A are:
* operation mad jackal
* five costumes for jill
* the botique key
* the next game save.
* and one extra epilogue for Chris Redfield, Barry Burton, Leon Scott Kennedy, Claire Redfield, Sherry Birkin, Ada Wong and Hunk
this information is from Alias ChandooG FAQ