Hi Morpheuss,
A 640/Q47 is a solid score (it's just shy of the 80th percentile overall) and it is considerably better than a 580, so you should apply to any Schools that interest you. You have to remember that Business Schools look at your OVERALL application, so you need to show the proper qualifications AND present yourself properly.
Since you don't appear to know which Schools you'll be applying to, there's no real way to assess your 'chances.' Think about what you want an MBA to do for YOU, then research the various programs that 'match up' with your goals. You might need to retake the GMAT and you might even need to push your applications to Round 2, but for something as significant as an MBA, that level of adjustment is something that you have to be comfortable with.
GMAT assassins aren't born, they're made,
Rich