Hi ConquertheGMAT,
First off, a 640 is a solid score (it's just shy of the 80th percentile overall), so it might be enough to get you into your first choice Business School. Since you were able to raise your score 100 points your own, it stands to reason that you could probably raise your scores further though (with the proper resources and some additional study time).
I'll be happy to offer some suggestions, but I'd like to know a bit more about your studies and your goals first:
1) How long have you studied?
2) What materials have you used?
3) When are your application deadlines?
4) Do you know which Schools you're planning to apply to?
GMAT assassins aren't born, they're made,
Rich