This article is from the Final-Fantasy and other Square Soft Games FAQ, by email@example.com (Nick Zitzmann) with numerous contributions by others.
No. Nothing you do in the flashback has an effect on the rest of the
game, nor can you get Vincent or Tifa's 'Final Heaven' manual during the
flashback. The only exception is, if you explore Tifa's house and look
in her closet, read her letters, etc., she will dislike you for doing